Logslim – compact test/build output before your AI agent reads it

Logslim, an open-source CLI and GitHub Action, reduces test and build log output by 80-95% for AI agents and human reviewers, compacting noisy CI logs into structured failure summaries with fix hints. The tool, available as an MIT-licensed npm package, deduplicates repeated warnings, collapses stack frames, and posts readable PR comments, saving tokens when agents like Claude Code or Cursor read test output.

CI failed? Get a 5-line PR summary — not a 400-line Actions log. Agent reading test output? Cut 80–95% of the tokens. When tests or builds fail, you scroll GitHub Actions logs. When Claude Code or Cursor runs npm test , the agent reads everything — progress bars, 120 identical warnings, 40 frames of node modules . logslim fixes both: CI / humans — GitHub Action posts structured failures on your PR file, line, fix hints Agents / tokens — CLI + MCP compacts noisy output before an LLM reads it ~80–95% savings on failures npx logslim -- npm test No account. No API key. MIT open source. When CI fails, post a readable summary on the pull request instead of making reviewers dig through Actions logs. permissions: contents: read pull-requests: write jobs: test: runs-on: ubuntu-latest steps: - uses: actions/checkout@v4 - uses: actions/setup-node@v4 with: node-version: 20 - run: npm ci - name: Run tests id: test run: npm test 2 &1 | tee test-output.log continue-on-error: true - name: Post failure summary if: steps.test.outcome == 'failure' && github.event name == 'pull request' uses: P156HAM/logslim/action@v0.3.0 with: log-file: test-output.log exit-code: 1 github-token: ${{ secrets.GITHUB TOKEN }} - name: Fail job if: steps.test.outcome == 'failure' run: exit 1 What gets posted on the PR: - Structured failures with file:line and messages - Fix hints for known codes TS2339 , ERESOLVE , … - Link to the full CI log - Token/log reduction stats useful when agents also read the output The Action uses the same engine as the CLI — compaction, error extraction, and code cards. You get human-readable PR comments and agent-ready JSON from one tool. | Input | Default | Purpose | |---|---|---| log-file | required | Path to captured test/build log | exit-code | 1 | Exit code of the failed command | github-token | required | secrets.GITHUB TOKEN with pull-requests: write | logslim-version | 0.3.0 | npm version to run | skip-on-success | true | Don't comment when no failure detected | git clone https://github.com/P156HAM/logslim.git cd logslim && npm install && npm run build && npm run demo Or without cloning: js npx logslim -- node -e "console.log 'ok' ; for let i=0;i<30;i++ console.log 'warn '+i ; throw Error 'fail' " BEFORE — what the agent reads today ~18 lines here; real runs are 500–3000 : PASS src/utils.test.ts console.warn deprecated prop id=1000 console.warn deprecated prop id=1001 console.warn deprecated prop id=1002 ... same warning ×120 FAIL src/checkout/cart.test.ts Expected: 89.10 Received: 99.00 at cart.test.ts:48:27 at node modules/jest-circus/build/utils.js:298:28 at node modules/jest-circus/build/utils.js:231:10 at node modules/jest-circus/build/run.js:252:3 ... 15 more node modules frames Test Suites: 1 failed, 1 passed, 2 total AFTER — what logslim gives the agent: PASS src/utils.test.ts console.warn deprecated prop id=1000 console.warn deprecated prop id=1001 console.warn deprecated prop id=1002 +5 similar lines omitted by logslim FAIL src/checkout/cart.test.ts Expected: 89.10 Received: 99.00 at cart.test.ts:48:27 at node modules/jest-circus/build/utils.js:298:28 … 3 vendor/internal frames collapsed by logslim Test Suites: 1 failed, 1 passed, 2 total Same failure. Same fix. ~ 92% fewer tokens . npm test ──► logslim ──► agent / CI / you │ ├─ 1. Strip ANSI colors & spinner garbage ├─ 2. Dedupe repeated lines warn spam ├─ 3. Collapse node modules stack frames ├─ 4. Group similar lines timestamps/ids masked ├─ 5. Extract structured errors file, line, message ├─ 6. Attach fix cards for known codes TS2339, ERESOLVE… └─ 7. Optional token budget trim middle, keep errors Failure mode default : tests pass → light cleanup only. Tests fail → full pipeline. You only pay the compaction cost when something actually broke. Every removed section is marked in place +47 similar lines omitted by logslim so the agent knows data was elided and can re-run the raw command if needed. npm install -g logslim or zero-install: npx logslim -- npm test Requires Node 18+. logslim -- npm test logslim -- python -m pytest -x logslim -- npx tsc --noEmit Exit code is preserved. Output on stdout is compacted. Stats on stderr. npm test 2 &1 | logslim npm test; logslim --exit-code $? 2 &1 < full.log if you saved output logslim --json -- npm test { "exitCode": 1, "failed": true, "compacted": "FAIL src/checkout/cart.test.ts\n...", "errors": { "file": "cart.test.ts", "line": 48, "message": "Expected: 89.10, Received: 99.00", "kind": "assertion" } , "codes": { "id": "TS2339", "lang": "typescript", "meaning": "Property does not exist on type", "fix steps": "Check for typos", "Extend the interface", "Use optional chaining" } , "stats": { "tokensIn": 3296, "tokensOut": 252, "saved": 0.92, "applied": "full" } } The agent reads compacted + errors + codes — not thousands of lines of prose. logslim --json --attach git,ci -- npm test Prepends: branch: feat/x | commit: a3f2c1d | pr: 42 from GITHUB env vars . | Flag | What it does | |---|---| --mode failure | Compact hard only on failure default | --mode full | Always compact hard | --mode light | Strip ANSI only, never aggressive dedupe | --json | Structured output see above | --attach git,ci | Prepend branch/commit/CI metadata | --budget 2000 | Hard token cap; errors + head/tail survive | --exit-code N | For pipe mode when you know the exit code | --no-codes | Skip error code fix cards | --no-stats | Hide stderr savings footer | Lets the agent call compaction as a tool — no manual piping. Project .mcp.json or Claude Desktop config: { "mcpServers": { "logslim": { "command": "npx", "args": "-y", "logslim-mcp" } } } Tool: compact output — pass output raw log text and optional exit code . Returns compacted text, extracted errors, fix cards, and stats. Local dev: npm run build && npm run mcp Add to CLAUDE.md , AGENTS.md , or .cursor/rules : When running tests, builds, or linters that produce verbose output: - Prefer: logslim --mode failure --json -- <command - Read the compacted , errors , and codes fields before debugging. - If output was elided, re-run the raw command only if you need full logs. When logs contain known codes, logslim attaches a short fix card ~30 tokens instead of making the agent guess or search docs. | Family | Examples | Source | |---|---|---| | TypeScript | TS2339, TS2554, TS2307 | errors/typescript.json | | Node | ECONNREFUSED, ENOTFOUND | errors/node.json | | npm | ERESOLVE, ELIFECYCLE | errors/npm.json | Hand-curated pocket references — not scraped docs. PRs welcome to add codes. | Log type | Lines | Tokens | Saved | |---|---|---|---| | Jest warn spam + 1 failure | 149 → 25 | ~3,300 → ~250 | 92% | | Webpack build asset noise + 2 TS errors | 548 → 55 | ~8,900 → ~1,000 | 88% | | Pytest 25 identical failures | 356 → 153 | ~4,300 → ~1,500 | 64% | Token counts are estimated ~4 chars/token . Good for relative savings, not billing. js import { compact, process } from "logslim"; const { text, stats } = compact rawLog, { mode: "failure", exitCode: 1 } ; const result = process rawLog, { mode: "failure", exitCode: 1, attach: "git", "ci" , } ; // result.text, result.errors, result.codes, result.stats | Use it | Skip it | |---|---| | CI failed and you want a PR summary, not a 400-line log | Tests passed and output is already short | | AI agents running tests/builds locally or in CI | You already tee full logs to disk for audit | | Long repetitive failure output jest, pytest, webpack | Platform already truncates well enough for you | | MCP workflows where tool output hits context limits | You need full logs for compliance archive | Keep full logs if you need them: npm test 2 &1 | tee full.log | logslim npm install npm test npm run build npm run demo logslim gets sharper every time it learns a new error code or a new log format — and both are easy first contributions: Add an error fix card TypeScript / Node / npm — a ~5-minute, pure-JSON PR. Share a log that compacts badly — paste real output from a tool logslim mangles. Add support for a new runner — Playwright, pytest, vitest, cargo, gradle… Start here: good first issues · CONTRIBUTING.md /P156HAM/logslim/blob/main/CONTRIBUTING.md MIT — use freely, no account required.