Trim what bloats your AI coding context. Claude Code, Cursor, and Codex send your files as context on every request — so a lockfile, a dist/ bundle, or a big JSON quietly makes every message cost more. ctxtrim finds that junk and writes the ignore files that cut it.
npx ctxtrim # see what's costing you tokens
npx ctxtrim --write # write .cursorignore + .aiexclude to cut it
AI coding tools re-send your context with every turn — "a one-line question in a session that's been open all day still draws usage for the whole conversation," and large context can cost 3× the tokens. Usage dashboards (like ccusage) tell you how much you spent after the fact. ctxtrim is the other half: it tells you what to stop sending so the bill is smaller in the first place.
It flags the files that are high-cost and low-value for a model — lockfiles, dist//build/ output, node_modules, minified bundles, big data/JSON, generated code — and generates the ignore files your tools already honor.
ctxtrim · my-repo · 412 files
Full context load: ~1.2M tokens (~$3.61 @ $3/M input)
Trimmable: ~890k tokens (73%) → save ~$2.67 per load
by category: lockfile 410k · vendored 260k · data 140k · build 80k
Top offenders
~410k $1.23 package-lock.json — dependency lockfile
~180k $0.54 data/cities.json — large json (180k tokens)
~80k $0.24 dist/ — build / generated output directory
...
✓ .cursorignore (created, 34 patterns), .aiexclude (created, 34 patterns)
Estimates use the widely-cited ~4-chars-per-token rule (great for ranking and relative savings; pass --price to match your model).
npx ctxtrim [path] [options]
npx ctxtrim # report on the current repo
npx ctxtrim --write # write .cursorignore + .aiexclude
npx ctxtrim ./repo --price 15 # estimate at Opus-tier input pricing
npx ctxtrim --format json # machine-readable
npx ctxtrim --fail-on-waste 40 # CI: exit 1 if 40%+ of context is junk| Flag | Default | Meaning |
|---|---|---|
--write |
off | create/update the ignore files (otherwise report only) |
--targets <list> |
cursor,gemini |
cursor→.cursorignore, gemini→.aiexclude, generic→.aiignore |
--price <usd> |
3 |
$ per 1M input tokens for the estimate |
--max-tokens <n> |
2000 |
a file over this counts as "large" data |
--top <n> |
12 |
offenders to list |
--format <text|json> |
text |
|
--fail-on-waste <pct> |
— | exit 1 if trimmable context ≥ pct (CI gate) |
Ignore files it writes (all real formats the tools honor): .cursorignore (Cursor), .aiexclude (Gemini Code Assist / Firebase Studio), .aiignore (generic). Writes are idempotent — a managed block between markers, so your own rules are preserved and re-runs just update the block.
- A fast, deterministic, zero-dependency heuristic — no model calls, nothing uploaded.
- It won't touch source you actually want seen — run it on a lean repo and it says "already lean ✓".
- Token counts are estimates for ranking and savings math, not billing-exact.
- It writes ignore files; it never deletes anything.
Pairs with ctxlens (profiles a running agent's context) — ctxtrim is the static, pre-emptive half. Part of a small agent-tooling set alongside skill-audit and mcp-audit.
MIT