lain

name

lain

description

Structural code intelligence for AI coding agents. Use this skill when the user wants to understand how a codebase is organized (modules, call graphs, file dependencies), find where to start reading, trace the impact of a change, find code by meaning, or understand what a symbol does in its full context. Do NOT use this skill for simple file reading or trivial tasks that don't require understanding structural relationships.

lain — Codebase Intelligence

The lain MCP server is available at tool prefix mcp__lain__*. The server indexes the workspace and exposes tools for structural queries, semantic search, and code navigation.

1. When to use lain

Prefer lain when the question is about structure:

• "Where should I start reading this codebase?"
• "What does X depend on?" / "Who calls X?"
• "If I change X, what else breaks?"
• "Where do we do X?" (semantic search by meaning)
• "What is this function/class doing?"
• "Is there unused code?"
• "What files change together?"

Skip lain for simple file reads or single-line searches.

2. The most useful tools

Tool	When to use it
mcp__lain__get_health	First call in any session.
mcp__lain__find_anchors	"Where should I start reading?" — most-called, most-stable symbols.
mcp__lain__list_entry_points	Find main()s and entry points.
mcp__lain__explore_architecture	High-level module/file tree.
mcp__lain__get_blast_radius	"If I change X, what breaks?" — transitive callers.
mcp__lain__trace_dependency	"What does X depend on?"
mcp__lain__semantic_search	Find code by meaning: "error handling", "rate limiting", etc. Body excerpts included.
mcp__lain__explain_symbol	"What is this symbol?" — source + callers + callees + anchor.
mcp__lain__find_dead_code	Unused definitions (filters false positives).
mcp__lain__get_coupling_radar	"What files change with X?"

3. Workflows

"I'm new here, where do I start?"

1. get_health
2. find_anchors limit=5
3. explain_symbol <top anchor>
4. get_blast_radius <top anchor>

"I'm about to refactor X"

1. get_blast_radius <X> depth=2
2. trace_dependency <X>
3. get_coupling_radar <X path>

"Where do we do X?" (semantic)

1. semantic_search <natural query> limit=5
2. explain_symbol <top result>

4. Caveats

• Cold-query latency: first call after server start is 5-10s (loads bge embedding, runs cross-encoder reranker). Don't panic. Subsequent calls are sub-second.
• Workspace scope: lain is bound to the workspace passed at install time. For other repos, re-run the install.
• get_call_chain may hang in v0.4.0 (known bug). Use trace_dependency and get_blast_radius instead.

5. Don't

• Don't use semantic_search with literal symbol names. Use natural language: "where do we retry failed uploads" not "retry_upload".
• Don't ask lain to analyze a different repo — workspace is hardcoded.
• Don't repeatedly call get_health — once per session is enough.