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Posts structured failure summaries on pull requests when CI fails, including file, line, fix hints, and token reduction stats.

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.

npm license node

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.

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/action@v0.4.0
        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

Related MCP server: PlanckBot

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

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

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.

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.

Measured savings

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.

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

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

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.

logslim-mcp