fastapi-lsp

Language server for FastAPI and Starlette — routes, Depends() graph, url_for, Jinja templates, env/settings. One Rust binary, any LSP-capable editor. Static analysis only.

Features


Diagnostics	param mismatches, shadowed routes, unincluded routers, `Depends(fn())`, dep cycles, broken `url_for`, missing templates, undefined env keys
Navigation	test call → handler, `Depends()` chains both ways, template files, `.env` lines
Hover	route card: resolved path, router chain, response model, deps, middleware
Completions	route paths, `url_for` names, template paths, env keys
Symbols	`GET /api/books/{book_id}` in the symbol picker
Code lenses	test count, dep usage, override count per handler
`check` CLI	same diagnostics as a linter — `fastapi-lsp check .`

Installation

uv tool install fastapi-lsp

Or with pip:

pip install fastapi-lsp

Or download a pre-built binary from the releases page.

Editor setup

Neovim

vim.lsp.config('fastapi_lsp', {
  cmd = { 'fastapi-lsp', '--stdio' },
  filetypes = { 'python', 'html', 'htmldjango' },
  root_markers = { 'pyproject.toml', '.git' },
})
vim.lsp.enable('fastapi_lsp')

Helix

# ~/.config/helix/languages.toml
[language-server.fastapi-lsp]
command = "fastapi-lsp"
args = ["--stdio"]

[[language]]
name = "python"
language-servers = ["pyright", "fastapi-lsp"]

[[language]]
name = "html"
language-servers = ["vscode-html-language-server", "fastapi-lsp"]

[[language]]
name = "jinja"
language-servers = ["fastapi-lsp"]

Zed

Install from the Zed extensions panel (Cmd+Shift+X) — search for fastapi-lsp and click Install. It activates automatically for Python, HTML, and Jinja2 files.

To control server order alongside other language servers or pass initialization options, add to ~/.config/zed/settings.json:

{
  "languages": { "Python": { "language_servers": ["fastapi-lsp", "..."] } },
  "lsp": { "fastapi-lsp": { "initialization_options": { "templates": ["app/templates"] } } }
}

Configuration

Zero config for standard projects. Priority: InitializationOptions › fastapi-lsp.toml › [tool.fastapi-lsp] in pyproject.toml.

Option	Default
`entrypoint`	(auto-detected)	main app file
`templates`	`[]`	Jinja template directories
`source_roots`	`[]`	extra import resolution roots
`env_files`	`[".env", ".env.example"]`	env key definitions
`settings_env_files`	`[".env", ".env.example", ".env.unittest"]`	env files checked for `BaseSettings` coverage
`process_env`	`false`	include server process env
`process_env_show_values`	`false`	show process-env values in hover
`client_fixtures`	`["client", "async_client"]`	pytest HTTP client fixture names
`env.ignore`	`[]`	env keys to suppress from diagnostics
`scan.ignore`	`[".beads", ".claude", ".codegraph", ".git", ".mypy_cache", ".playwright-mcp", ".pytest_cache", ".ruff_cache", ".venv", "__pycache__", "node_modules", "target"]`	directory names excluded from workspace scans (replaces, not extends, the default)

Feature toggles — all true by default except test_unknown_paths:

Toggle	Default
`diagnostics`	`true`
`completion`	`true`
`hover`	`true`
`navigation`	`true`
`code_actions`	`true`
`code_lens`	`true`
`symbols`	`true`
`inlay_hints`	`true`
`document_links`	`true`
`test_unknown_paths`	`false`

# fastapi-lsp.toml
entrypoint = "app/main.py"
templates = ["app/templates"]

[features]
code_lens = false

[check]
only = []
ignore = ["env/undefined-key"]

[scan]
ignore = [".beads", ".claude", ".codegraph", ".git", ".mypy_cache", ".playwright-mcp", ".pytest_cache", ".ruff_cache", ".venv", "__pycache__", "node_modules", "target", ".worktrees"]

CLI

fastapi-lsp lsp [--stdio | --tcp --address 127.0.0.1 --port 9257]
fastapi-lsp check PATH [--only CODES] [--ignore CODES] [--format text|json] [--fix]
fastapi-lsp routes [PATH] [--format text|json]

Development

cargo build
cargo test
uv run --group dev pytest e2e/ -v

License

MIT