| 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.
