logslim

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:

1. CI / humans — GitHub Action posts structured failures on your PR (file, line, fix hints)
2. 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.

GitHub Action — PR failure summary

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/[email protected]
        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.

See it work (30 seconds)

git clone https://github.com/P156HAM/logslim.git
cd logslim && npm install && npm run build && npm run demo

Or without cloning:

npx logslim -- node -e "console.log('ok'); for(let i=0;i<30;i++)console.log('warn '+i); throw Error('fail')"

Before → After

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.

How it works

  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.

Install

npm install -g logslim
# or zero-install:
npx logslim -- npm test

Requires Node 18+.

Usage

Basic — wrap any command

logslim -- npm test
logslim -- python -m pytest -x
logslim -- npx tsc --noEmit

Exit code is preserved. Output on stdout is compacted. Stats on stderr.

Pipe mode

npm test 2>&1 | logslim
npm test; logslim --exit-code $? 2>&1 < full.log   # if you saved output

JSON — for agents and CI

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.

CI context (GitHub Actions)

logslim --json --attach git,ci -- npm test

Prepends: branch: feat/x | commit: a3f2c1d | pr: #42 (from GITHUB_* env vars).

All options

MCP server (Claude Code / Cursor)

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

Tell your agent to use it

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.

Error code fix cards

When logs contain known codes, logslim attaches a short fix card (~30 tokens)
instead of making the agent guess or search docs.

Hand-curated pocket references — not scraped docs. PRs welcome to add codes.

Measured savings

Token counts are estimated (~4 chars/token). Good for relative savings, not billing.

Library API

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

When to use logslim

Keep full logs if you need them:

npm test 2>&1 | tee full.log | logslim

Development

npm install
npm test
npm run build
npm run demo

Contributing

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

License

MIT — use freely, no account required.