Lsp Setup

LSP Setup

Enable LSP-based code navigation in a repository by creating an agent card with LSP function tools.

Prerequisites

• Python: ty language server (uv tool install ty)
• TypeScript: typescript-language-server (npm install -g typescript-language-server typescript)
• Rust: rust-analyzer (rustup component add rust-analyzer)

The multilspy package is included with fast-agent.

Setup Steps

1. Examine the Repository

Before copying files, inspect the repo root:

ls -d */
ls pyproject.toml tsconfig.json package.json 2>/dev/null
ls Cargo.toml 2>/dev/null

Identify:

• Language: Python (pyproject.toml), TypeScript (tsconfig.json), or Rust (Cargo.toml)
• Source directories: Common patterns are src/, lib/, app/, tests/, packages/, apps/, crates/, examples/, benches/
• Root-level files you may want to query: setup.py, manage.py, conftest.py, build.rs, etc.
• Any existing .fast-agent/ setup

2. Create Directory Structure

IMPORTANT -- Use the fast-agent environment directory if specified. The default is .fast-agent/.

mkdir -p .fast-agent/agent-cards

3. Create or update the card files

Do not blindly overwrite an existing .fast-agent/agent-cards/dev.md.

If dev.md does not exist yet

Create it from this skill's language-specific template:

Python:

• assets/python/dev.md → .fast-agent/agent-cards/dev.md
• assets/python/multilspy_tools.py → .fast-agent/agent-cards/multilspy_tools.py

TypeScript:

• assets/typescript/dev.md → .fast-agent/agent-cards/dev.md
• assets/typescript/multilspy_tools.py → .fast-agent/agent-cards/multilspy_tools.py

Rust:

• assets/rust/dev.md → .fast-agent/agent-cards/dev.md
• assets/rust/rust_lsp_tools.py → .fast-agent/agent-cards/rust_lsp_tools.py

These starter templates default to model: $system.default. Only pin a model if the repo already has a good reason to do that.

If dev.md already exists

Edit it in place and preserve the existing card configuration.

Keep existing frontmatter values unless you have a specific reason to change them, especially:

• model
• default
• type
• shell
• existing hooks, servers, tools, and other card settings

Model handling is especially important:

• If the existing card already pins a specific model, keep it.
• If the existing card already uses model: $system.default, keep that too.
• If you are creating a new card from scratch, prefer model: $system.default unless the repo explicitly needs a pinned model.

Only add the LSP function tools that are missing for the repo's language:

Python / TypeScript

function_tools:
  - multilspy_tools.py:lsp_hover
  - multilspy_tools.py:lsp_definition
  - multilspy_tools.py:lsp_references
  - multilspy_tools.py:lsp_document_symbols
  - multilspy_tools.py:lsp_workspace_symbols
  - multilspy_tools.py:lsp_diagnostics

Rust

function_tools:
  - rust_lsp_tools.py:lsp_hover
  - rust_lsp_tools.py:lsp_definition
  - rust_lsp_tools.py:lsp_references
  - rust_lsp_tools.py:lsp_document_symbols
  - rust_lsp_tools.py:lsp_workspace_symbols
  - rust_lsp_tools.py:lsp_diagnostics

Do not remove unrelated instructions from the existing prompt body just to add LSP support.

DO Add a navigation hint to the card if appropriate.

Use LSP tools for structural queries: definitions, references, symbols, hover info, diagnostics.
For broad text discovery or file operations, use whatever search tool or card is already available in this environment.

4. Configure the helper module

For Python and TypeScript, configure multilspy_tools.py. For Rust, configure rust_lsp_tools.py.

There are two different configuration steps:

Required: verify _REPO_ROOT

The LSP server normally just needs the correct repo root as cwd / rootUri to work well. Make sure _REPO_ROOT matches where you placed the card:

# .fast-agent/agent-cards/ = 2 levels below repo root
_REPO_ROOT = Path(__file__).resolve().parents[2]

If you place the card somewhere else, adjust parents[...] accordingly.

Recommended: set _ALLOWED_DIRS and _ALLOWED_FILES

These settings are wrapper policy, not an LSP requirement. They control what files the tool is allowed to query.

_ALLOWED_DIRS = {"src", "tests"}
_ALLOWED_FILES = {"conftest.py"}

Common patterns:

• Standard Python: {"src", "tests", "test", "examples"}
• Standard TypeScript: {"src"}
• Monorepo: {"packages", "apps", "libs"}
• Django: {"app", "apps", "tests"} + {"manage.py"}
• Flat repo / allow entire repo: {"."}

Use narrower allowlists when possible. Use {"."} only when whole-repo access is worth the tradeoff.

Rust note

For Rust, always verify the executable itself, not just its PATH entry:

command -v rust-analyzer
rust-analyzer --version

Use the Cargo workspace root for _REPO_ROOT whenever possible, especially for crates/* layouts.

5. Verify Setup

fast-agent go

Try:

• show me the symbols in src/main.py
• find the definition of Foo in src/foo.py at line 12
• show me the symbols in crates/my_crate/src/lib.rs

Adjust the path to a real file in the repo.

Troubleshooting

Run fast-agent check to diagnose issues.

• "ty is not available on PATH": Install ty (uv tool install ty)
• "typescript-language-server is not available": Install via npm
• "rust-analyzer is not available on PATH": Install it with rustup component add rust-analyzer
• "Path must live under...": Update _ALLOWED_DIRS or _ALLOWED_FILES
• "Path is outside the repository root": Check _REPO_ROOT
• LSP starts but results are poor: Confirm the repo root has the right pyproject.toml, tsconfig.json, workspace layout, and dependencies

Source: fast-agent-ai/skills — distributed by TomeVault.