lainBLOCK

A code graph for coding agents. Lain maps callers, dependencies, symbols, and Git co-changes, then exposes them through the Model Context Protocol (MCP). Before an agent edits a function, it can inspect what depends on it and how the rest of the code reaches it.

The demo traces a symbol across the bytes and tokio repositories. Agents query the same graph through MCP; the browser shows what Lain indexed and where an answer came from.

Ask your agent:

If I change validate_token, what breaks?
Show me the call chain from entry to helper_a.
Which files usually change with auth.rs?
Is another agent already editing this code?

Lain answers with symbol names and source paths from a local index. The index stays on disk between runs and can cover more than one repository. It follows commits, not uncommitted edits: after committing, a re-index pass (lain reindex or a fresh session) brings it current — and answers that may miss recent work say so instead of going quiet. Semantic search is optional; graph queries work without an embedding model.

Install

Using the release installer:

curl -fsSL https://raw.githubusercontent.com/spuentesp/lain/main/install.sh | bash
source ~/.zshrc   # or ~/.bashrc
lain --version

Rust 1.89 or newer is only needed when building from source. The quickstart covers non-interactive installation and the optional local embedding model.

Connect an agent

Run one setup command from the repository you want Lain to index:

lain setup --agent claude-code
lain setup --agent codex
lain setup --agent cursor
lain setup --agent vscode
lain setup --agent continue

Use lain setup --agent generic for another MCP host. It writes this project-level .mcp.json, with the absolute path of the lain binary that ran setup as command:

{
"mcpServers": {
"lain": {
"command": "/home/you/.local/bin/lain",