ClickHouse MCP Server
An MCP server for ClickHouse.
The server implements MCP 2026-07-28 and supports legacy initialize handshakes from
2024-11-05 through 2025-11-25. Modern clients use sessionless requests and
server/discover. Existing clients can continue to negotiate the legacy protocol.
[!NOTE]
HTTP requests without MCP-Protocol-Version are routed through legacy handling so
clients from before 2025-06-18 can continue to connect. MCP 2026-07-28 permits
this behavior on servers that support those clients. Modern clients should send the
header on every POST request.
Features
ClickHouse Tools
ClickHouse tool responses are JSON-encoded strings. Integers outside
[-9007199254740991, 9007199254740991] are returned as decimal strings to preserve exact
values in JavaScript clients. This applies to query rows and integer table metadata. Safe-range
integers and booleans keep their JSON types.
-
run_query
- Execute SQL queries on your ClickHouse cluster.
- Input:
query (string): The SQL query to execute.
- Optional input:
params (object): Named values for ClickHouse {name:Type} placeholders. See Query parameters.
- Queries run in read-only mode by default (
CLICKHOUSE_ALLOW_WRITE_ACCESS=false), but writes can be enabled explicitly if needed.
DESCRIBE (<query>) and EXPLAIN ESTIMATE <query> run here too and are optional ways to inspect a query's result schema or its estimated reads. See Checking a query before running it.
-
list_databases
- List all databases on your ClickHouse cluster.
-
list_tables
- List tables in a database with pagination.
- Required input:
database (string).
- Optional inputs:
like / not_like (string): Apply LIKE or NOT LIKE filters to table names.page_token (string): Single-use token returned by a previous call. It is retained for up to one hour.page_size (int, default 50): Number of tables returned per page; must be greater than 0.include_detailed_columns (bool, default true): When false, omits column metadata for lighter responses while keeping the full create_table_query.
- Response shape:
tables: Array of table objects for the current page.next_page_token: Pass this single-use value back before it expires to fetch the next page, or null when there are no more tables.total_tables: Total count of tables that match the supplied filters.
Agents Schema discovery
The server instructions suggest reading Agents Schema's
canonical AGENTS.ROOT through run_query when list_databases reveals an AGENTS
database, before writing analytical SQL. This is guidance for the agent: no metadata
is fetched automatically, tool results are unchanged, and existing ClickHouse
permissions still apply. If AGENTS.ROOT is missing or inaccessible, normal discovery
and queries remain available.
Query parameters
Pass values separately from SQL through the optional params object:
{
"query": "SELECT {id:UInt32} AS id, {name:String} AS name",
"params": {"id": 13, "name": "O'Reilly"}
}
Use ClickHouse's {name:Type} placeholders without quoting them. Keep the opening
brace, name, and colon adjacent, as in {id:UInt32}. Spaces after the colon and
within the type are supported, as in {id: UInt32} and {amount:Decimal(18, 4)}.
For compatibility across supported driver versions, start names with a letter or
underscore and use only letters, digits, and underscores.
Python-style %s or %(name)s formatting and the driver's $name$ raw binary
parameters are not supported. Calls with only query still work. Omitting params,
passing null, or passing an empty object leaves the query unbound.
Parameter values can be JSON strings, numbers, booleans, null, or arrays, provided
they match the declared ClickHouse type:
- Use
null with a Nullable(...) type.
- Pass exact integers outside JavaScript's safe range as decimal strings, for
example
"18446744073709551615" with {id:UInt64}. Dates, timestamps, and exact
decimals can also be passed as strings with the corresponding ClickHouse type.
- Bind vectors as one array, for example
{vector:Array(Float32)} with
"params": {"vector": [0.25, 0.5, 0.75]}.
- Nulls inside arrays depend on the installed driver. They work with
clickhouse-connect 1.8.0 but fail with the supported minimum 1.0.0.
- JSON lists and objects cannot bind to ClickHouse
Tuple and Map types.
Missing values and incompatible types return query errors. With non-empty params,
a query carrying many unterminated {name: placeholder starts is rejected, including
placeholder-like text in comments or string literals.
Parameterized queries use the same write protection, timeouts, cancellation, and
JSON result encoding as other queries.
Parameter values stay out of the MCP server's normal SQL log messages, but remain
in MCP tool arguments and may appear in backend errors. ClickHouse 26.3.20.7
substitutes values into the query text in system.query_log, system.processes,
and system.text_log. Parameter binding is not a privacy feature and does not
reduce the number of vector values sent in a tool call.
Checking a query before running it
run_query also runs DESCRIBE and EXPLAIN ESTIMATE. Both are optional checks: reach for DESCRIBE when you need a query's output columns and types, and for EXPLAIN ESTIMATE before a SELECT that could be expensive.
DESCRIBE (<query>) inspects the result schema and returns the same output-column metadata as DESCRIBE TABLE:
DESCRIBE (SELECT user, sum(amt) FROM events WHERE ts > now() - INTERVAL 30 DAY GROUP BY user)
user String
sum(amt) Decimal(38, 2)
ClickHouse has to analyze the query to answer, so analysis errors surface here, with ClickHouse's own message, instead of part way through execution:
DESCRIBE (SELECT usr FROM events) -> Code: 47. Unknown expression identifier `usr` ... Maybe you meant: ['user']
DESCRIBE (SELECT * FROM nosuch) -> Code: 60. Unknown table expression identifier 'nosuch'
A query that describes cleanly can still fail when it runs, on a memory limit or a remote server error, and it says nothing about cost.
EXPLAIN ESTIMATE <query> returns the parts, rows and marks the query would read, one row per table, which is what separates a primary key lookup from a full scan:
EXPLAIN ESTIMATE SELECT count() FROM events WHERE id = 42
database table parts rows marks
default events 1 8192 1
Those are estimated reads from MergeTree family tables, after primary key and partition pruning. They are not run time and not result size, and other table engines are not covered.
Neither statement runs the query body, but analysis is not always free: DESCRIBE (SELECT (SELECT sleep(1))) executes the scalar subquery while analyzing. Both are read-only and work under the default CLICKHOUSE_ALLOW_WRITE_ACCESS=false. See the ClickHouse documentation for EXPLAIN ESTIMATE and DESCRIBE.
chDB Tools
run_chdb_select_query
- Execute SQL queries using chDB's embedded ClickHouse engine.
- Input:
query (string): The SQL query to execute.
- Integers outside
[-9007199254740991, 9007199254740991] are returned as decimal strings.
- Query data directly from various sources (files, URLs, databases) without ETL processes.
- Requires the optional
chdb extra: pip install 'mcp-clickhouse[chdb]'
Health Check Endpoint
When running with HTTP or SSE transport, a health check endpoint is available at /health. This endpoint:
- Returns
200 OK (body: OK) if the server is healthy and can connect to ClickHouse
- Returns
503 Service Unavailable with a generic error message if the server cannot connect to ClickHouse
- Returns
503 if a ClickHouse probe does not finish within two seconds. Concurrent requests share one in-flight probe
- Reuses a completed probe result for one second, so probes that arrive in quick succession do not each connect to ClickHouse. A failure or a recovery can therefore be reported up to a second late
GET and HEAD requests to the endpoint are intentionally unauthenticated and exempt from Host and Origin validation so orchestrator probes (e.g. Kubernetes liveness/readiness, load balancers) can use runtime-assigned pod or target IPs without extra configuration. /health is reserved and cannot be used as the MCP transport path. The response body is deliberately minimal to avoid leaking backend version strings or error details; debug failures via the server logs.
Example:
curl http://localhost:8000/health
# Response: OK
Security
Authentication for HTTP/SSE Transports
When using HTTP or SSE transport, authentication is required by default. The stdio transport (default) does not require authentication as it only communicates via standard input/output.
Three authentication modes are supported. Pick one:
| Mode | When to use | Env var |
|---|
| Static bearer token | Simple deployments, internal services | CLICKHOUSE_MCP_AUTH_TOKEN |
| OAuth / OIDC (via FastMCP) | Azure Entra, Google, GitHub, WorkOS, etc. | FASTMCP_SERVER_AUTH=<provider-class-path> (+ provider-specific FASTMCP_SERVER_AUTH_* vars) |
| Disabled | Local development only | CLICKHOUSE_MCP_AUTH_DISABLED=true |
Startup fails if none of these are configured for HTTP/SSE transports.
Setting Up Authentication
-
Generate a secure token (can be any random string):
# Using uuidgen (macOS/Linux)
uuidgen
# Using openssl
openssl rand -hex 32
-
Configure the server with the token:
export CLICKHOUSE_MCP_AUTH_TOKEN="your-generated-token"
-
Configure your MCP client to include the token in requests:
For Claude Desktop with HTTP/SSE transport:
{
"mcpServers": {
"mcp-clickhouse": {
"url": "http://127.0.0.1:8000",
"headers": {
"Authorization": "Bearer your-generated-token"
}
}
}
}
Note: the /health endpoint is intentionally unauthenticated (see Health Check Endpoint above). To verify that bearer-token auth is actually rejecting unauthenticated requests, hit the MCP endpoint itself e.g. with the MCP Inspector, or by POSTing a JSON-RPC request to /mcp with and without the Authorization header and confirming the unauthenticated call returns 401.
OAuth / OIDC via FastMCP
For production deployments with identity providers (Azure Entra, Google, GitHub, WorkOS, etc.), delegate authentication to FastMCP's built-in auth providers instead of using a static token. Set FASTMCP_SERVER_AUTH to the full class path of a FastMCP auth provider, along with the provider-specific FASTMCP_SERVER_AUTH_* variables, and leave CLICKHOUSE_MCP_AUTH_TOKEN unset.
Example (Azure Entra):
export FASTMCP_SERVER_AUTH=fastmcp.server.auth.providers.azure.AzureProvider
export FASTMCP_SERVER_AUTH_AZURE_TENANT_ID="<tenant-id>"
export FASTMCP_SERVER_AUTH_AZURE_CLIENT_ID="<client-id>"
export FASTMCP_SERVER_AUTH_AZURE_CLIENT_SECRET="<client-secret>"
export FASTMCP_SERVER_AUTH_AZURE_BASE_URL="https://mcp.example.com"
export FASTMCP_SERVER_AUTH_AZURE_REQUIRED_SCOPES="read access_as_user"
mcp-clickhouse retains these FastMCP 2.14.7 environment prefixes for the FastMCP 4.0.0
built-in providers:
| Provider class path | Provider variable prefix |
|---|
fastmcp.server.auth.providers.auth0.Auth0Provider | FASTMCP_SERVER_AUTH_AUTH0_ |
fastmcp.server.auth.providers.aws.AWSCognitoProvider | FASTMCP_SERVER_AUTH_AWS_COGNITO_ |
fastmcp.server.auth.providers.azure.AzureProvider | FASTMCP_SERVER_AUTH_AZURE_ |
fastmcp.server.auth.providers.descope.DescopeProvider | FASTMCP_SERVER_AUTH_DESCOPEPROVIDER_ |
fastmcp.server.auth.providers.discord.DiscordProvider | FASTMCP_SERVER_AUTH_DISCORD_ |
fastmcp.server.auth.providers.github.GitHubProvider | FASTMCP_SERVER_AUTH_GITHUB_ |
fastmcp.server.auth.providers.google.GoogleProvider | FASTMCP_SERVER_AUTH_GOOGLE_ |
fastmcp.server.auth.providers.introspection.IntrospectionTokenVerifier | FASTMCP_SERVER_AUTH_INTROSPECTION_ |
fastmcp.server.auth.providers.jwt.JWTVerifier | FASTMCP_SERVER_AUTH_JWT_ |
fastmcp.server.auth.providers.oci.OCIProvider | FASTMCP_SERVER_AUTH_OCI_ |
fastmcp.server.auth.providers.scalekit.ScalekitProvider | FASTMCP_SERVER_AUTH_SCALEKITPROVIDER_ |
fastmcp.server.auth.providers.supabase.SupabaseProvider | FASTMCP_SERVER_AUTH_SUPABASE_ |
fastmcp.server.auth.providers.workos.WorkOSProvider | FASTMCP_SERVER_AUTH_WORKOS_ |
fastmcp.server.auth.providers.workos.AuthKitProvider | FASTMCP_SERVER_AUTH_AUTHKITPROVIDER_ |
Append the uppercase provider field name to the prefix. See the
FastMCP docs for each provider's configuration
requirements.
Auth values set directly in the process environment take precedence case-insensitively.
The default .env load starts at the installed mcp_clickhouse package directory,
resolves symlinks first, and walks upward to the filesystem root. It loads the first
.env it finds and loads nothing if there is none. It never reads the working
directory, regardless of how the server is launched. A source checkout normally finds
the repository root .env. That file may also provide FASTMCP_SERVER_AUTH and its
provider fields. Its values take precedence over the explicit or compatibility auth
file.
For FastMCP 2 compatibility, mcp-clickhouse reads missing provider fields from .env
in the working directory, but that compatibility fallback cannot select
FASTMCP_SERVER_AUTH. A process-set FASTMCP_ENV_FILE replaces that compatibility
fallback and may provide both the selector and provider fields. Set it before startup.
The mcp-clickhouse compatibility loader reads only FASTMCP_SERVER_AUTH and
FASTMCP_SERVER_AUTH_* from that file, so it cannot inject CLICKHOUSE_* settings.
FastMCP 4 may use the same file for its own broader settings. A custom provider receives
no environment-derived constructor arguments and must support no-argument construction.
Treat both discovered and working-directory .env files as trusted authentication
configuration. Anyone who can create or write a .env in any directory from the package
directory up to the filesystem root can control which file is discovered, select the
provider, and set its fields. Anyone who can write the working-directory file controls every provider
field absent from the process and discovered configuration, including signing keys,
issuers and endpoints, and client secrets. A process-set FASTMCP_ENV_FILE that points
to an operator-owned file disables the working-directory fallback.
FastMCP 4 changed the default OAuth proxy client store. Deployments that relied on
FastMCP 2's default OAuth proxy storage must have clients register and authorize again.
Compatible custom storage, static bearer tokens, and JWT verification are unaffected.
Development Mode (Disabling Authentication)
For local development and testing only, you can disable authentication by setting:
export CLICKHOUSE_MCP_AUTH_DISABLED=true
export CLICKHOUSE_MCP_ALLOWED_HOSTS=127.0.0.1:8000,localhost:8000
WARNING: Only use this for local development. Do not disable authentication when the server is exposed to any network.
Custom Middleware
You can add custom middleware to the MCP server without modifying the source code. FastMCP provides a middleware system that allows you to intercept and process MCP protocol messages (tool calls, resource reads, prompts, etc.).
How to Use
- Create a Python module with middleware classes extending
Middleware and a setup_middleware(mcp) function:
# my_middleware.py
import logging
from fastmcp.server.middleware import Middleware, MiddlewareContext, CallNext
logger = logging.getLogger("my-middleware")
class LoggingMiddleware(Middleware):
"""Log all tool calls."""
async def on_call_tool(self, context: MiddlewareContext, call_next: CallNext):
tool_name = context.message.name if hasattr(context.message, 'name') else 'unknown'
logger.info(f"Calling tool: {tool_name}")
result = await call_next(context)
logger.info(f"Tool {tool_name} completed")
return result
def setup_middleware(mcp):
"""Register middleware with the MCP server."""
mcp.add_middleware(LoggingMiddleware())
- Set the
MCP_MIDDLEWARE_MODULE environment variable to the module name (without .py extension):
{
"mcpServers": {
"mcp-clickhouse": {
"command": "uv",
"args": ["run", "--with", "mcp-clickhouse", "--python", "3.12", "mcp-clickhouse"],
"env": {
"CLICKHOUSE_HOST": "<clickhouse-host>",
"CLICKHOUSE_USER": "<clickhouse-user>",
"CLICKHOUSE_PASSWORD": "<clickhouse-password>",
"MCP_MIDDLEWARE_MODULE": "my_middleware"
}
}
}
}
- Ensure your middleware module is in Python's import path (e.g., in the same directory where the MCP server runs, or installed as a package).
Example Middleware
An example middleware module is provided in example_middleware.py showing common patterns:
- Logging all MCP requests
- Logging tool calls specifically
- Measuring request processing time
To use the example:
"env": {
"MCP_MIDDLEWARE_MODULE": "example_middleware"
}
Middleware Capabilities
The Middleware base class provides hooks for different MCP operations:
on_message(context, call_next) - Called for all messageson_request(context, call_next) - Called for all requestson_notification(context, call_next) - Called for all notificationson_call_tool(context, call_next) - Called when a tool is executedon_read_resource(context, call_next) - Called when a resource is readon_get_prompt(context, call_next) - Called when a prompt is retrievedon_list_tools(context, call_next) - Called when listing toolson_list_resources(context, call_next) - Called when listing resourceson_list_resource_templates(context, call_next) - Called when listing resource templateson_list_prompts(context, call_next) - Called when listing prompts
Each hook receives a MiddlewareContext object containing the message and metadata, and a call_next function to continue the pipeline.
Dynamic Client Configuration via Context State
Middleware can override ClickHouse client configuration on a per-request basis using the CLIENT_CONFIG_OVERRIDES_KEY context state key. The server merges these overrides with the base configuration from environment variables.
from fastmcp.server.dependencies import get_context
from fastmcp.server.middleware import CallNext, Middleware, MiddlewareContext
from mcp_clickhouse.mcp_server import CLIENT_CONFIG_OVERRIDES_KEY
class ClientConfigMiddleware(Middleware):
async def on_call_tool(self, context: MiddlewareContext, call_next: CallNext):
ctx = get_context()
await ctx.set_state(
CLIENT_CONFIG_OVERRIDES_KEY,
{
"connect_timeout": 60,
"send_receive_timeout": 120,
},
serializable=False,
)
return await call_next(context)
This enables advanced use cases like dynamic timeout adjustments, tenant-specific routing, or per-user connection settings.
The state value must be a dictionary. Nested settings and generic_args values must be
mappings and are merged with the base configuration. Invalid values fail the tool call before
a ClickHouse client is created. CLICKHOUSE_ROLE remains active unless the override explicitly
supplies settings.role. Top-level role and ch_role keys, plus the same keys under
generic_args, are rejected.
Set verify, ca_cert, client_cert, client_cert_key, tls_mode, server_host_name,
and pool_mgr only as top-level overrides. They cannot be nested under generic_args. A
custom pool_mgr cannot be combined with managed CA or client certificate settings. DSN query
parameters cannot set these keys, and a DSN cannot select the chdb backend. Use explicit
top-level host, port, username, password, database, and secure overrides to change
the connection. A forwarded DSN does not replace populated base connection fields or select
TLS. It can fill empty fields and supply supported query parameters such as query_limit.
secure and verify overrides accept booleans or the strings true and false.
verify also accepts proxy, which behaves as
tls_mode: proxy when tls_mode is unset and therefore uses Basic authentication with the
environment password. A secure override selects the matching https or http interface and
does not change the port. An explicit interface override must be http or https and agree
with secure. After merging overrides, default and mutual client certificate modes omit the
password. proxy and strict modes use Basic authentication with the environment password
unless the override supplies its own credentials.
Treat these overrides as trusted middleware input. Middleware must authenticate and authorize
request-derived values before setting them. Use serializable=False so FastMCP keeps the
value in request-local state. The default serializable=True stores session state and is
rejected by the server. The server snapshots the value before dispatching blocking database
work. Do not store tenant data in session-scoped Context state. A rejected session-scoped
override remains attached to a legacy MCP session and causes later tool calls in that session
to fail until the client reconnects. A per-request ClickHouse role is connection configuration,
not a tenant authorization boundary. Enforce tenant isolation with ClickHouse users, roles,
and grants.
Development
-
In test-services directory run docker compose up -d to start the ClickHouse cluster.
-
Add the following variables to a .env file in the root of the repository.
Note: The use of the default user in this context is intended solely for local development purposes.
CLICKHOUSE_HOST=localhost
CLICKHOUSE_PORT=8123
CLICKHOUSE_USER=default
CLICKHOUSE_PASSWORD=clickhouse
-
Run uv sync to install the dependencies. To install uv follow the instructions here. Then do source .venv/bin/activate.
-
For easy testing with the MCP Inspector, run uv run fastmcp dev inspector mcp_clickhouse/mcp_server.py:mcp to start the MCP server.
-
To test with HTTP transport and the health check endpoint:
# For development, disable authentication
CLICKHOUSE_MCP_SERVER_TRANSPORT=http CLICKHOUSE_MCP_AUTH_DISABLED=true CLICKHOUSE_MCP_ALLOWED_HOSTS=127.0.0.1:8000,localhost:8000 python -m mcp_clickhouse.main
# Or with authentication (generate a token first)
CLICKHOUSE_MCP_SERVER_TRANSPORT=http CLICKHOUSE_MCP_AUTH_TOKEN="your-token" python -m mcp_clickhouse.main
# Then in another terminal:
curl http://localhost:8000/health
Code layout
The package uses a flat module layout. Start with mcp_server.py
for server assembly and registration, then follow the implementation into its owning module.
| Module | Responsibility |
|---|
| mcp_server.py, main.py | Startup assembly, tool and prompt registration, shutdown coordination, and CLI startup |
| clients.py | Request configuration, cached ClickHouse connections, and client leases |
| queries.py | Query execution, cancellation, and destructive-operation guards |
| metadata.py | Database and table discovery, metadata models, and pagination |
| chdb_backend.py, chdb_prompt.py | Optional chDB initialization, query execution, and prompt content |
| health.py, executors.py | Health probes and caching, and the worker pools used by server operations |
| auth.py, transport.py, http_security.py | Dotenv loading, authentication, HTTP/SSE app construction, and Host/Origin validation |
| mcp_env.py, serialization.py | Environment configuration and JSON result encoding |
| mcp_middleware_hook.py, skills_advisor.py | Custom middleware loading and server instructions |
Each server assembly owns its worker pools, client cache, active queries, pagination cache,
health state, and chDB backend. Worker and client cleanup runs at process exit. Package imports
initialize the default server, including when first importing an extracted module.
In tests, patch the module or owner instance where the code reads a dependency. For example,
patch mcp_clickhouse.clients.clickhouse_connect.get_client for client creation. Compatibility
imports in mcp_server.py can be separate bindings from the ones an implementation uses.
Environment Variables
Configuration is split into independent groups. Mixing them up is a common cause of hard-to-debug connection failures:
| Group | Variables | Controls |
|---|
| ClickHouse database connection | CLICKHOUSE_HOST, CLICKHOUSE_PORT, CLICKHOUSE_SECURE, CLICKHOUSE_VERIFY, certificate variables | How this MCP server connects to your ClickHouse cluster over the HTTP interface |
| MCP server / transport | CLICKHOUSE_MCP_*, FASTMCP_SERVER_AUTH, FASTMCP_SERVER_AUTH_*, FASTMCP_ENV_FILE | MCP transport, authentication, and query-tool execution limits |
| Middleware / chDB | MCP_MIDDLEWARE_MODULE, CHDB_* | Optional extensions |
[!IMPORTANT]
CLICKHOUSE_SECURE, CLICKHOUSE_VERIFY, CLICKHOUSE_CA_CERT, CLICKHOUSE_CLIENT_CERT, CLICKHOUSE_CLIENT_CERT_KEY, CLICKHOUSE_TLS_MODE, and CLICKHOUSE_PORT apply to the outbound ClickHouse database connection only. They do not configure TLS, client certificates, ports, or authentication for the inbound MCP HTTP/SSE endpoint.
Example: if the MCP server runs in Kubernetes behind an ingress that terminates TLS, that is an MCP transport concern. Keep CLICKHOUSE_SECURE aligned with how the pod reaches ClickHouse itself (HTTPS → true, plain HTTP → false). Setting CLICKHOUSE_SECURE=false because the MCP server is behind an ingress will make the server dial ClickHouse over HTTP—often against an HTTPS-only port—and produce opaque HTTP/TLS errors in the server logs.
ClickHouse database connection
These variables configure the clickhouse-connect HTTP client and the behavior of ClickHouse-backed tools such as run_query, list_databases, and list_tables.
mcp-clickhouse requires clickhouse-connect 1.x, starting with 1.0.0.
Required Variables
CLICKHOUSE_HOST: The hostname of your ClickHouse server (database endpoint, not the MCP server bind address)CLICKHOUSE_USER: The username for ClickHouse authenticationCLICKHOUSE_PASSWORD: The password for ClickHouse authentication
- Required unless
CLICKHOUSE_CLIENT_CERT uses the default or "mutual" TLS mode
- In default or
"mutual" mode, certificate authentication is used and the password is not sent
[!CAUTION]
It is important to treat your MCP database user as you would any external client connecting to your database, granting only the minimum necessary privileges required for its operation. The use of default or administrative users should be strictly avoided at all times.
Optional Variables
CLICKHOUSE_PORT: HTTP interface port of your ClickHouse server
- Default:
8443 if CLICKHOUSE_SECURE=true, 8123 if CLICKHOUSE_SECURE=false
- Usually doesn't need to be set unless using a non-standard port
- Must be an HTTP interface port, not the native TCP protocol port used by
clickhouse-client
- Common values:
- HTTP:
8123 (plain) / 8443 (TLS) — used by this server and ClickHouse Cloud HTTPS
- Native TCP (not supported here):
9000 (plain) / 9440 (TLS) — used by clickhouse-client
- If the server responds with
Port 9000 is for clickhouse-client program, you are pointed at the native protocol; switch to the HTTP port (8123/8443 or your deployment's HTTP mapping)
CLICKHOUSE_ROLE: The ClickHouse role to use for authentication
- Default: None
- Set this if your user requires a specific role
CLICKHOUSE_SECURE: Enable HTTPS for the ClickHouse database connection (not for MCP clients)
- Default:
"true"
- Set to
"false" only when the MCP server reaches ClickHouse over plain HTTP (typical for local Docker Compose on port 8123)
- Leave
"true" for ClickHouse Cloud and any HTTPS database endpoint—even if the MCP server itself is exposed via HTTP, stdio, or an ingress that terminates TLS separately
- Mismatching this flag with the database port (e.g.
CLICKHOUSE_SECURE=false against port 8443) is a frequent setup mistake and usually surfaces as confusing HTTP client errors rather than a clear "wrong scheme" message
CLICKHOUSE_VERIFY: Enable/disable SSL certificate verification for the ClickHouse HTTPS connection
- Default:
"true"
- Set to
"false" to disable certificate verification (not recommended for production)
- TLS certificates: The package uses your operating system trust store via
truststore.inject_into_ssl() at startup. Python's default SSL handling is used if injection is disabled with MCP_CLICKHOUSE_TRUSTSTORE_DISABLE=1 or fails.
MCP_CLICKHOUSE_TRUSTSTORE_DISABLE: Disable the process-wide operating system trust store integration for TLS
- Default: unset (trust store integration is enabled)
- Set to exactly
"1" before startup to skip truststore.inject_into_ssl() and use Python's default SSL certificate handling. Other values do not disable the integration.
- This does not disable certificate verification.
CLICKHOUSE_VERIFY still controls verification for the ClickHouse HTTPS connection.
CLICKHOUSE_CA_CERT: Path to a PEM CA certificate bundle for the ClickHouse HTTPS connection
- Default: None (uses the operating system trust store unless truststore injection is disabled or fails)
- Use this by itself when a ClickHouse server or private proxy presents a certificate signed by a private CA. This changes server certificate verification and does not enable client certificate authentication.
- Requires
CLICKHOUSE_SECURE=true and CLICKHOUSE_VERIFY=true
CLICKHOUSE_CLIENT_CERT: Path to a PEM client certificate for the ClickHouse HTTPS connection
- Default: None
- The file may also contain the private key. Otherwise set
CLICKHOUSE_CLIENT_CERT_KEY.
- The ClickHouse user still comes from
CLICKHOUSE_USER.
CLICKHOUSE_CLIENT_CERT_KEY: Path to the PEM private key for CLICKHOUSE_CLIENT_CERT
- Default: None
- Optional when the private key is included in the client certificate file
- Cannot be used without
CLICKHOUSE_CLIENT_CERT
CLICKHOUSE_TLS_MODE: How clickhouse-connect uses CLICKHOUSE_CLIENT_CERT
- Default: None, which behaves as
"mutual" when a client certificate is set
"mutual": Use the client certificate for ClickHouse X.509 user authentication. CLICKHOUSE_PASSWORD is optional and is not sent."proxy": Present the client certificate to a TLS-terminating proxy, then use ClickHouse Basic authentication. CLICKHOUSE_PASSWORD is required."strict": Present the client certificate because the ClickHouse server requires one at the TLS layer, then use ClickHouse Basic authentication. CLICKHOUSE_PASSWORD is required. This mode does not strengthen server certificate verification. CLICKHOUSE_VERIFY controls that verification.- clickhouse-connect treats
"proxy" and "strict" identically. The two names document intent.
- Values are trimmed and case-insensitive. A blank value is treated as unset. Other values are rejected before a ClickHouse client is created, on the first ClickHouse tool call or
/health probe.
- Requires
CLICKHOUSE_CLIENT_CERT. All client certificate options require CLICKHOUSE_SECURE=true.
CLICKHOUSE_SERVER_HOST_NAME: Server hostname for SNI override and certificate validation on the ClickHouse connection
- Default: None (uses the connection hostname)
- This is useful when connecting through proxies or load balancers where the certificate hostname differs from the connection hostname. When set, this hostname will be used for both SNI (Server Name Indication) during the TLS handshake and for certificate hostname validation.
CLICKHOUSE_PROXY_PATH: URL path prefix for the ClickHouse HTTP endpoint
- Default: None
- Set this when the ClickHouse HTTP interface is exposed behind a reverse proxy under a path prefix (for example,
/clickhouse)
CLICKHOUSE_CONNECT_TIMEOUT: Connection timeout in seconds for the ClickHouse client
- Default:
"30"
- Increase this value if you experience connection timeouts
CLICKHOUSE_SEND_RECEIVE_TIMEOUT: Send/receive timeout in seconds for the ClickHouse client
- Default: the lower of
300 or CLICKHOUSE_MCP_QUERY_TIMEOUT + 5, so worker threads unblock shortly after a query timeout
- If explicitly set, the value is used as-is (e.g.
"300" for long-running queries)
CLICKHOUSE_DATABASE: Default ClickHouse database to use
- Default: None (uses server default)
- Set this to automatically connect to a specific database
CLICKHOUSE_ENABLED: Enable/disable ClickHouse database tools
- Default:
"true"
- Set to
"false" to disable ClickHouse tools when using chDB only
CLICKHOUSE_ALLOW_WRITE_ACCESS: Allow write operations (DDL and DML) against ClickHouse
- Default:
"false"
- Set to
"true" to allow non-destructive DDL and DML (CREATE, INSERT, ALTER ADD COLUMN). Destructive statements additionally need CLICKHOUSE_ALLOW_DROP=true
- When disabled (default), queries run with
readonly=1 setting to prevent data modifications
CLICKHOUSE_ALLOW_DROP: Allow destructive operations (any DROP or TRUNCATE, DELETE and UPDATE including the ALTER TABLE variants, REPLACE TABLE / REPLACE PARTITION / CREATE OR REPLACE, CLEAR COLUMN / CLEAR INDEX / CLEAR PROJECTION, and DETACH ... PERMANENTLY)
- Default:
"false"
- Only takes effect when
CLICKHOUSE_ALLOW_WRITE_ACCESS=true is also set
- This gate is a best-effort accident guard in the MCP server, not a security boundary. Restrict the ClickHouse user's grants for real enforcement (see Destructive Operation Protection)
ClickHouse TLS certificate files
The certificate variables contain file paths, not PEM contents. mcp-clickhouse passes these
paths to clickhouse-connect. For Docker or Kubernetes, mount the certificate and private key
as read-only files and use their paths inside the container. Do not bake a private key into an
image, commit it to source control, or put its contents in an environment variable.
In mutual mode, the configured client certificate identifies this mcp-clickhouse process as
CLICKHOUSE_USER. It does not authenticate inbound MCP clients or pass their identities to
ClickHouse. Configure MCP transport authentication separately.
Restart mcp-clickhouse after replacing a certificate or key at the same path when immediate
rotation or revocation is required. Cached clients can retain existing TLS connections, and
the cache does not track file contents or modification times.
ClickHouse Cloud does not support X.509 client certificate authentication for database users.
Use CLICKHOUSE_USER and CLICKHOUSE_PASSWORD for ClickHouse Cloud. A CA certificate can
still be useful when a private proxy in front of an endpoint presents a certificate signed by
a private CA.
MCP server and transport
These variables control the MCP process itself, including transport, authentication, and query-tool execution limits. They are independent of the ClickHouse database settings above. See also Authentication for HTTP/SSE Transports.
CLICKHOUSE_MCP_SERVER_TRANSPORT: Sets the transport method for the MCP server
- Default:
"stdio"
- Valid options:
"stdio", "http", "sse". This is useful for local development with tools like MCP Inspector.
stdio is typical for Claude Desktop; http/sse expose a network listener (bind host/port below)"sse" selects the deprecated standalone HTTP+SSE transport and logs a warning. Use "http" for Streamable HTTP in new deployments.
CLICKHOUSE_MCP_BIND_HOST: Host to bind the MCP server to when using HTTP or SSE transport
- Default:
"127.0.0.1"
- Set to
"0.0.0.0" to bind to all network interfaces (useful for Docker or remote access)
- Only used when transport is
"http" or "sse" — not related to CLICKHOUSE_HOST
CLICKHOUSE_MCP_BIND_PORT: Port to bind the MCP server to when using HTTP or SSE transport
- Default:
"8000"
- Only used when transport is
"http" or "sse" — not related to CLICKHOUSE_PORT
CLICKHOUSE_MCP_QUERY_TIMEOUT: Timeout in seconds for query tool calls
- Default:
"30"
- Increase this if you see
Query timed out after ... errors for heavy queries
- When a query times out, the server attempts to cancel it with
KILL QUERY
- Unless
CLICKHOUSE_SEND_RECEIVE_TIMEOUT is explicitly set, the HTTP read timeout is capped at this value plus five seconds
CLICKHOUSE_MCP_MAX_WORKERS: Maximum number of concurrent query worker threads
- Default:
"10"
- Increase if your workload requires many concurrent tool calls
- Metadata tools use a separate pool with
min(4, CLICKHOUSE_MCP_MAX_WORKERS) threads so schema discovery cannot delay queries
CLICKHOUSE_MCP_AUTH_TOKEN: Static bearer token for HTTP/SSE transports
- Default: None
- One of
CLICKHOUSE_MCP_AUTH_TOKEN, FASTMCP_SERVER_AUTH, or CLICKHOUSE_MCP_AUTH_DISABLED=true is required for HTTP/SSE transports
- Generate using
uuidgen or openssl rand -hex 32
- Clients must send this token in the
Authorization: Bearer <token> header
FASTMCP_SERVER_AUTH: Delegate authentication to a FastMCP auth provider
- Default: None
- Value is the full class path of an AuthProvider subclass, e.g.
fastmcp.server.auth.providers.azure.AzureProvider or fastmcp.server.auth.providers.google.GoogleProvider
- When set, mcp-clickhouse loads the provider from the existing
FASTMCP_SERVER_AUTH_* environment variables; leave CLICKHOUSE_MCP_AUTH_TOKEN unset in this mode
- Custom providers receive no environment-derived constructor arguments and must support no-argument construction
- FastMCP 4 no longer supports Supabase HS256 verification. Supabase deployments must use RS256 or ES256.
FASTMCP_ENV_FILE: Optional file containing FASTMCP_SERVER_AUTH and provider-specific environment variables
- Default: None. When unset, the compatibility loader reads missing provider fields from
.env in the working directory. It does not read FASTMCP_SERVER_AUTH from that fallback
- Set it in the process environment before startup. A value loaded from the default
.env cannot redirect the compatibility loader
- If process-set, this file may provide both
FASTMCP_SERVER_AUTH and provider fields and replaces the working-directory fallback
- Process environment values take precedence case-insensitively
- The mcp-clickhouse compatibility loader reads this file only when building HTTP/SSE authentication and reads only
FASTMCP_SERVER_AUTH and FASTMCP_SERVER_AUTH_* entries. FastMCP 4 may read the same file for its broader settings
- The default
.env load is separate. It starts at the installed mcp_clickhouse package directory, resolves symlinks, walks upward to the filesystem root, and loads the first .env found or nothing. It never reads the working directory, regardless of launch method. That file may provide FASTMCP_SERVER_AUTH and provider fields along with other server settings. A source checkout normally finds the repository root .env
CLICKHOUSE_MCP_AUTH_DISABLED: Disable authentication for HTTP/SSE transports
- Default:
"false" (authentication is enabled)
- Set to
"true" to disable authentication for local development/testing only
- WARNING: Only use for local development. Do not disable when exposed to networks
CLICKHOUSE_MCP_ALLOWED_HOSTS: Comma separated Host header values the HTTP/SSE server answers for
- Default for a loopback bind: bare and any-port forms of
127.0.0.1, localhost, and [::1]
- If set, the value must contain at least one Host entry.
- A concrete non-loopback bind address defaults to that address and the configured port. A wildcard bind such as
0.0.0.0 or :: requires an explicit non-empty value because the public Host cannot be inferred.
- Host validation is a defense in depth against DNS rebinding. Origin validation below is required separately by MCP.
- Entries are exact (
localhost:8000) or accept any port (localhost:*). Example: CLICKHOUSE_MCP_ALLOWED_HOSTS=127.0.0.1:8000,localhost:8000
- The
host:* form matches only values that carry a port. A port-less Host (a standard-port deployment where the client omits :80/:443) must be listed as a bare exact entry (example.com) as well.
- Requests with a non-matching or missing
Host header get 421 Misdirected Request. GET and HEAD requests to /health are exempt from Host and Origin validation so orchestrator probes keep working.
- Behind a reverse proxy, prefer preserving the original
Host header. You can instead list the upstream Host value the proxy sends. Set an explicit list when a launcher such as fastmcp run overrides the bind address for remote access.
- mcp-clickhouse forces FastMCP's separate Host and Origin guard off.
FASTMCP_HTTP_HOST_ORIGIN_PROTECTION, FASTMCP_HTTP_ALLOWED_HOSTS, and FASTMCP_HTTP_ALLOWED_ORIGINS do not apply. CLICKHOUSE_MCP_ALLOWED_HOSTS and CLICKHOUSE_MCP_ALLOWED_ORIGINS are authoritative.
CLICKHOUSE_MCP_TRUSTED_PROXIES: Proxy IP addresses or CIDR networks whose X-Forwarded-* headers are trusted
- Default: None.
X-Forwarded-Host is ignored. Existing Uvicorn handling of X-Forwarded-For and X-Forwarded-Proto is unchanged.
- Entries must be IP addresses or CIDR networks, such as
127.0.0.1,10.20.0.0/24,2001:db8::1. CIDRs must use their network address, so 10.20.0.1/24 is rejected. Host names, scoped IPv6 addresses, *, 0.0.0.0/0, and ::/0 are also rejected.
- Trust is based on the immediate raw socket peer. A request from any other peer, or a request without a client address, ignores
X-Forwarded-Host and validates Host.
- A trusted peer may send exactly one
X-Forwarded-Host header containing one non-empty value. Duplicate fields, empty values, and comma separated lists get 421 Misdirected Request. If the header is absent, Host is validated.
- Use the narrowest possible address or network. The MCP server must only be reachable through proxies in the configured ranges. Every trusted proxy must strip and overwrite client supplied
X-Forwarded-Host and X-Forwarded-Proto values, and construct X-Forwarded-For from the verified connection peer.
- The built-in server and
fastmcp run disable Uvicorn's outer proxy-header handling, validate Host from the raw peer, then apply X-Forwarded-For and X-Forwarded-Proto. Explicitly enabling uvicorn_config["proxy_headers"] fails startup in this mode.
- Direct ASGI embedding must disable proxy-header handling in the outer ASGI server and call
mcp.http_app(raw_client_address_preserved=True). Without that explicit assertion, app construction fails when trusted proxies are configured.
CLICKHOUSE_MCP_ALLOWED_ORIGINS: Comma separated Origin header values accepted on HTTP/SSE
- Default: None, which rejects every request that carries an
Origin header
- MCP requires Origin validation for HTTP/SSE transport connections. Requests without an Origin are accepted because non-browser MCP clients normally omit it. A non-matching Origin gets
403 Forbidden. The /health endpoint is exempt as described above.
- Entries are exact (
http://localhost:3000) or accept any port (http://localhost:*). As with hosts, the any-port form matches only origins that carry a port; a standard-port origin (https://app.example.com) must be listed exactly.
Reverse proxy Host handling
Preserve Host when possible. This keeps forwarded Host trust disabled:
location / {
proxy_pass http://mcp-clickhouse:8000;
proxy_set_header Host $http_host;
proxy_set_header X-Forwarded-Host "";
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header X-Forwarded-Proto $scheme;
}
Sanitize X-Forwarded-For and X-Forwarded-Proto independently of X-Forwarded-Host trust. Uvicorn may trust those headers based on the proxy peer even when CLICKHOUSE_MCP_TRUSTED_PROXIES is unset.
CLICKHOUSE_MCP_ALLOWED_HOSTS=mcp.example.com
Stock nginx changes Host to the upstream name for proxied requests. It does not create or overwrite X-Forwarded-Host. If preserving Host is not possible, overwrite the forwarded header at the trusted edge:
location / {
proxy_pass http://mcp-clickhouse:8000;
proxy_set_header X-Forwarded-Host $http_host;
proxy_set_header X-Forwarded-For $remote_addr;
proxy_set_header X-Forwarded-Proto $scheme;
}
CLICKHOUSE_MCP_ALLOWED_HOSTS=mcp.example.com
CLICKHOUSE_MCP_TRUSTED_PROXIES=10.20.0.8
The second configuration is safe only when 10.20.0.8 is the proxy's immediate source address, the server port is isolated from other clients, and nginx overwrites the incoming forwarding headers as shown. For a proxy chain, each trusted hop must discard unverified incoming values before constructing the new forwarding headers.
On an IPv6 or dual-stack bind, IPv4 proxies may appear as IPv4-mapped addresses such as ::ffff:10.20.0.8; these are matched against IPv4 entries automatically. Envoy's append_x_forwarded_host appends to an existing X-Forwarded-Host rather than overwriting it, producing a comma separated list that is rejected, so configure the trusted hop to overwrite the header instead. On Kubernetes with source NAT (for example externalTrafficPolicy: Cluster) the observed peer may be a node IP rather than the proxy pod, so trust the pod or node CIDR as appropriate; ingress-nginx overwrites both Host and X-Forwarded-Host itself.
Middleware Variables
MCP_MIDDLEWARE_MODULE: Python module name containing custom middleware to inject into the MCP server
- Default: None (no middleware loaded)
- Set to the module name (without
.py extension) of your middleware module
- The module must provide a
setup_middleware(mcp) function
- See Custom Middleware for details and examples
chDB Variables
CHDB_ENABLED: Enable/disable chDB functionality
- Default:
"false"
- Set to
"true" to enable chDB tools
- Requires installing the optional extra:
mcp-clickhouse[chdb]
CHDB_DATA_PATH: The path to the chDB data directory
- Default:
":memory:" (in-memory database)
- Use
:memory: for in-memory database
- Use a file path for persistent storage (e.g.,
/path/to/chdb/data)
Common configuration pitfalls
CLICKHOUSE_SECURE vs MCP / ingress TLS — Turning off CLICKHOUSE_SECURE because the MCP server sits behind Kubernetes ingress, a reverse proxy, or is reached over plain HTTP does not disable database TLS; it only changes how this process connects to ClickHouse. Configure ingress TLS separately from the database client settings.- Native protocol ports —
CLICKHOUSE_PORT must target ClickHouse's HTTP interface (8123/8443 by default). Ports 9000/9440 are for the native TCP protocol (clickhouse-client) and will not work with this server.
- Host confusion —
CLICKHOUSE_HOST is the database hostname. CLICKHOUSE_MCP_BIND_HOST is only the address the MCP HTTP/SSE server listens on.
Example Configurations
For local development with Docker:
# Required variables
CLICKHOUSE_HOST=localhost
CLICKHOUSE_USER=default
CLICKHOUSE_PASSWORD=clickhouse
# Optional: Override defaults for local development
CLICKHOUSE_SECURE=false # Uses port 8123 automatically
CLICKHOUSE_VERIFY=false
For ClickHouse Cloud:
# Required variables
CLICKHOUSE_HOST=your-instance.clickhouse.cloud
CLICKHOUSE_USER=default
CLICKHOUSE_PASSWORD=your-password
# Optional: These use secure defaults
# CLICKHOUSE_SECURE=true # Uses port 8443 automatically
# CLICKHOUSE_DATABASE=your_database
For ClickHouse SQL Playground:
CLICKHOUSE_HOST=sql-clickhouse.clickhouse.com
CLICKHOUSE_USER=demo
CLICKHOUSE_PASSWORD=
# Uses secure defaults (HTTPS on port 8443)
For a private server CA without client certificate authentication:
CLICKHOUSE_HOST=your-secure-clickhouse.example.com
CLICKHOUSE_USER=your-user
CLICKHOUSE_PASSWORD=your-password
CLICKHOUSE_SECURE=true
CLICKHOUSE_VERIFY=true
CLICKHOUSE_CA_CERT=/run/secrets/clickhouse-ca.pem
For ClickHouse X.509 client certificate authentication:
CLICKHOUSE_HOST=your-secure-clickhouse.example.com
CLICKHOUSE_USER=your-certificate-user
CLICKHOUSE_SECURE=true
CLICKHOUSE_CLIENT_CERT=/run/secrets/clickhouse-client.pem
CLICKHOUSE_CLIENT_CERT_KEY=/run/secrets/clickhouse-client-key.pem
# CLICKHOUSE_CA_CERT=/run/secrets/clickhouse-ca.pem # Only for a private server CA
# CLICKHOUSE_TLS_MODE=mutual # Optional. This is the default with a client certificate.
For a client certificate required by a strict TLS server while ClickHouse uses Basic
authentication:
CLICKHOUSE_HOST=your-secure-clickhouse.example.com
CLICKHOUSE_USER=your-user
CLICKHOUSE_PASSWORD=your-password
CLICKHOUSE_SECURE=true
CLICKHOUSE_CLIENT_CERT=/run/secrets/clickhouse-client.pem
CLICKHOUSE_CLIENT_CERT_KEY=/run/secrets/clickhouse-client-key.pem
CLICKHOUSE_TLS_MODE=strict
Use CLICKHOUSE_TLS_MODE=proxy instead when a TLS-terminating proxy requires the client
certificate and ClickHouse still uses Basic authentication.
For chDB only (in-memory):
# chDB configuration
CHDB_ENABLED=true
CLICKHOUSE_ENABLED=false
# CHDB_DATA_PATH defaults to :memory:
For chDB with persistent storage:
# chDB configuration
CHDB_ENABLED=true
CLICKHOUSE_ENABLED=false
CHDB_DATA_PATH=/path/to/chdb/data
For MCP Inspector or remote access with HTTP transport:
CLICKHOUSE_HOST=localhost
CLICKHOUSE_USER=default
CLICKHOUSE_PASSWORD=clickhouse
CLICKHOUSE_MCP_SERVER_TRANSPORT=http
CLICKHOUSE_MCP_BIND_HOST=0.0.0.0 # Bind to all interfaces
CLICKHOUSE_MCP_BIND_PORT=4200 # Custom port (default: 8000)
CLICKHOUSE_MCP_AUTH_TOKEN=your-generated-token # One auth mode required for HTTP/SSE (or FASTMCP_SERVER_AUTH, or CLICKHOUSE_MCP_AUTH_DISABLED=true)
CLICKHOUSE_MCP_ALLOWED_HOSTS=127.0.0.1:4200,localhost:4200,mcp.example.com:4200 # Include every Host value clients and proxies send
For local development with HTTP transport (authentication disabled):
CLICKHOUSE_HOST=localhost
CLICKHOUSE_USER=default
CLICKHOUSE_PASSWORD=clickhouse
CLICKHOUSE_MCP_SERVER_TRANSPORT=http
CLICKHOUSE_MCP_AUTH_DISABLED=true # Only for local development!
CLICKHOUSE_MCP_ALLOWED_HOSTS=127.0.0.1:8000,localhost:8000
When using HTTP transport, the server will run on the configured port (default 8000). For example, with the above configuration:
- MCP endpoint:
http://localhost:8000/mcp
- Health check:
http://localhost:8000/health
You can set these variables in your environment, in a .env file, or in the Claude Desktop configuration:
{
"mcpServers": {
"mcp-clickhouse": {
"command": "uv",
"args": [
"run",
"--with",
"mcp-clickhouse",
"--python",
"3.12",
"mcp-clickhouse"
],
"env": {
"CLICKHOUSE_HOST": "<clickhouse-host>",
"CLICKHOUSE_USER": "<clickhouse-user>",
"CLICKHOUSE_PASSWORD": "<clickhouse-password>",
"CLICKHOUSE_DATABASE": "<optional-database>",
"CLICKHOUSE_MCP_SERVER_TRANSPORT": "stdio",
"CLICKHOUSE_MCP_BIND_HOST": "127.0.0.1",
"CLICKHOUSE_MCP_BIND_PORT": "8000"
}
}
}
}
Note: The bind host and port settings are only used when transport is set to "http" or "sse".
Running tests
uv sync --all-extras --dev # install dev dependencies
uv run ruff check . # run linting
docker compose up -d test_services # start ClickHouse
uv run pytest -v tests
uv run pytest -v tests/test_tool.py # ClickHouse only
CHDB_ENABLED=true uv run --extra chdb pytest -v tests/test_chdb_tool.py # chDB only
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