Repo Map Skill

Agents burn their context windows on exploration: reading ten files to find the one, re-reading them next session, paying full price for code that was only ever navigation. The fix is the oldest one in computing — an index. This skill generates a compact, deterministic map (tree + line counts + top-level symbols via regex, no parser dependencies, nothing leaves the machine) and installs the discipline that makes it pay: read the map first, open only the files whose names and symbols match the task. The script prints its own economics: a typical map costs ~3% of reading everything.

What This Skill Produces

• The map — tree with per-file line counts and top-level symbols (functions, classes, types) for ~10 common languages
• The token math — reading-everything vs. reading-the-map, printed in the header
• The navigation plan — for the task at hand: which files the map says to open, which to skip
• The refresh rule — when the map is stale and what it costs to regenerate (nothing — it's local and instant)

Required Inputs

Ask for these if not provided:

• The directory — repo root or the subdirectory that matters (mapping src/ beats mapping node_modules' ancestors)
• The task — the map is generic; the navigation plan needs to know what's being hunted (a bug in auth? the payment flow? where X is defined?)
• Scale expectations — huge monorepos get mapped per-subdirectory (--max-files guards the map's own size; a 40,000-file map defeats itself)

Programmatic Helper

python3 scripts/repo_map.py .
python3 scripts/repo_map.py src --max-files 400 --max-symbols 8

Deterministic (sorted walk), stdlib-only, local. Skips .git, node_modules, build dirs. Symbols via per-language regex — deliberately humble: top-level names, not a full graph; the point is navigation, not analysis. Header prints files, lines, and the map-vs-everything token comparison.

Framework: The Navigation Discipline

1. Map before open, every exploration: the first act in an unfamiliar repo is the map, not a file read — one ~3%-cost artifact answers "what's here, what's it called, where would X live" for the whole session.
2. Open by match, not by curiosity: files get opened when their name or symbols match the task ("refund appears in billing/refunds.py → process_refund, RefundPolicy") — the map converts "read around and see" into a shortlist, and the shortlist is the saving.
3. The map is cache-friendly context: stable, deterministic output means the map can sit at the top of a session and stay byte-identical across turns — unlike raw file reads, it never invalidates a provider prefix cache by reordering.
4. Depth on demand: map → open the shortlisted file → if still lost, map the subdirectory deeper. Escalation is cheap because every level is local and instant; what's expensive is skipping the levels and reading wholesale.
5. Honest limits: regex symbols miss dynamic definitions, decorators' effects, and call graphs — for "who calls this," the map shortlists candidates and grep finishes the job. The map is the index, not the analysis; tools that build true graphs exist for the deep version (see Based On).

Output Format

Repo Map: [path] — [N] files, map ≈ [X]% of reading everything

[The script's map output]

Navigation Plan (for: [the task])

Open: [the shortlist, with the matching symbol/name per file] Skip: [the big directories the task doesn't touch] If not found: [the grep to run next, on the shortlist first]

Quality Checks

• The map was generated before any wholesale file reading
• The token comparison (map vs. everything) appears
• The navigation plan shortlists by name/symbol match with reasons
• Monorepos were mapped per-subdirectory, not defeated by their own size
• The regex-symbols limitation is stated when the task is call-graph-shaped

Anti-Patterns

• Do not read files to find out what's in them — that's the map's job at 3% of the price
• Do not regenerate the map every turn — it's stable; put it once at the session's top
• Do not oversell the symbols — top-level names, not semantics; grep and real parsers pick up where regex stops
• Do not map the world — --max-files and subdirectory scoping exist because a bloated map is just a slower file dump
• Do not skip the navigation plan — a map without a shortlist saved nothing yet

Based On

The codebase-as-index pattern — local knowledge graphs for agent navigation (as in Graphify, which does the full tree-sitter graph version) — distilled here into a zero-dependency, deterministic map with the read-the-map-first discipline.