SQLFluff MCP Server

sqlfluff-mcp-server

An MCP server that exposes SQLFluff's linting, fixing, and parsing over the Model Context Protocol, so any MCP-aware client (Claude, other agents, IDE integrations) can lint and fix SQL directly.

This project is independent of the SQLFluff maintainers — it's a thin wrapper around the public sqlfluff Python package.

Tools

Tool	Input	Config resolution
`lint_file`	path on disk	walks up from the file for `.sqlfluff` / `pyproject.toml` / etc.
`fix_file`	path on disk (+ `write` flag)	same directory walk
`parse_file`	path on disk	same directory walk
`lint_sql`	raw SQL text + `dialect`	none — dialect supplied explicitly
`fix_sql`	raw SQL text + `dialect`	none — dialect supplied explicitly
`parse_sql`	raw SQL text + `dialect`	none — dialect supplied explicitly
`list_dialects`	—	lists supported dialect names
`clear_config_cache`	—	clears SQLFluff's cached config-file contents

The *_file tools honor project config the same way the sqlfluff CLI does (via FluffConfig.from_path, which walks up the directory tree looking for .sqlfluff, pyproject.toml, setup.cfg, or tox.ini). The *_sql tools are for content that hasn't been written to disk (e.g. streamed from an editor buffer) and require you to pass dialect explicitly since there's no file location to resolve config from.

Config caching

SQLFluff caches the contents of config files it reads while walking a directory tree, for the lifetime of the process. Because this server is long-running (unlike the sqlfluff CLI, which is a fresh process per invocation), editing a .sqlfluff file after the server has started won't be picked up by lint_file / fix_file / parse_file until you call clear_config_cache. Call it whenever config on disk changes, or just proactively before a lint/fix/parse call if you're unsure.

Requirements

Python 3.10+
uv (recommended) or pipx/pip
mcp >=2.0.0,<3.0.0 and sqlfluff >=3.0.0 (installed automatically as dependencies — see Notes on dependencies)

Registering with an MCP client

This package is published on PyPI, so there's nothing to clone or install ahead of time. Point your MCP client's config (e.g. .claude.json / .mcp.json for Claude Code, or Claude Desktop's config file) at it via uvx, and it's fetched into an isolated cache and launched on demand:

{
  "mcpServers": {
    "sqlfluff": {
      "command": "uvx",
      "args": ["sqlfluff-mcp-server"]
    }
  }
}

No uv? pipx run sqlfluff-mcp-server as the command/args works the same way.

For stdio-based servers like this one, the client itself launches the process — automatically, when the client session starts, not when a prompt first needs it. Once it's registered, just ask the client to lint or fix a SQL file; the server is already running in the background and the tools are already available. If the server process crashes, the client restarts it for you.

Running it manually (for local testing/debugging)

uvx sqlfluff-mcp-server

This starts the server over stdio and blocks, waiting for an MCP client to speak the protocol to it on stdin/stdout — it's not something you'd run interactively day to day, just useful for sanity-checking the install or piping through the MCP Inspector.

Development

Clone the repo to work on the server itself (rather than just consuming it via uvx):

git clone <this-repo-url>
cd sqlfluff-mcp-server
uv sync --extra dev
uv run pytest
uv run ruff check .

To point an MCP client at your local checkout instead of the PyPI release (e.g. to test unreleased changes):

{
  "mcpServers": {
    "sqlfluff": {
      "command": "uv",
      "args": ["--directory", "/path/to/sqlfluff-mcp-server", "run", "sqlfluff-mcp-server"]
    }
  }
}

Notes on dependencies

mcp is pinned to >=2.0.0,<3.0.0. The SDK's 2.0 line renamed mcp.server.fastmcp.FastMCP to mcp.server.mcpserver.MCPServer and moved transport selection to run(transport=...); the @mcp.tool() decorator API is unchanged.
sqlfluff is left unpinned above 3.0.0 — SQLFluff releases fairly often and this server only depends on its stable Linter / FluffConfig API.

License

MIT — see LICENSE.

Documentation