Perch: Semantic Code Linting with Jev

TypeSafe has released Perch, a semantic code linting CLI installed via `npm install -g @lakeday/perch`, which scans source files and reports defects such as wrong_order, inverted_condition, off_by_one and unhandled_null with per-finding confidence scores and severity weights. The tool requires a PERCH_API_KEY from console.typesafe.ai, ranks findings worst-first through `perch issues`, re-checks fixes with `perch check`, and supports custom rules in perch.yaml plus assistant integrations for Claude Code, Codex, Pi and Cursor. A sample scan reported 20 problems across 5 files, all failing.

Semantic code linting with Jev. Create an API key at console.typesafe.ai https://console.typesafe.ai and set it as PERCH API KEY . npm install -g @lakeday/perch export PERCH API KEY=<your TypeSafe API key bash $ perch scan checkout.py ID Line Severity Type Confidence Problem Method bdc67421 14 P1 0.8 defect 81% wrong order place order ddc5c917 24 P1 0.8 defect 92% inverted condition can fulfil cart.py ID Line Severity Type Confidence Problem Method 287bfb9d 9 P1 1.0 defect 90% off by one subtotal 80d6ebbb 29 P1 1.4 defect 89% unhandled null cheapest ✖ 20 problems in 5 files, all failing perch issues lists them worst first. perch issues <id opens one up. perch check <id asks again after a fix, and records what it finds nowhere. perch setup claude-code .claude/skills/perch/SKILL.md perch setup codex .codex/skills/perch/SKILL.md perch setup pi .pi/skills/perch/SKILL.md perch setup cursor .cursor/rules/perch.mdc Extend perch with custom rules, in perch.yaml : - name: env-read-once where: "src/ / .js" each: method min: 70 ensure: This method takes its configuration as arguments. Reading process.env is the command line's job. | Getting started https://docs.perchscan.com/install/ | Install, the key, the first scan. | | Reading issues https://docs.perchscan.com/issues/ | The list, the filters, closing what does not matter. | | Semantic linting https://docs.perchscan.com/rules/ | where , each , sees , min , gate , and the longhand grammar. | | Checking a change https://docs.perchscan.com/check/ | perch check on work in progress. | | perch in CI https://docs.perchscan.com/ci/ | What a build can gate on, and what it cannot. | | Command reference https://docs.perchscan.com/cli/ | Every command, its flags, and what each exit code means. | | Inside a scan https://docs.perchscan.com/scan/ | The graph walk, the questions, and how probabilities turn into a ranking. | | Location | Contents | |---|---| | .perch/ | Generated scan results and cache files, alongside the committed files below. Use --out <directory to choose another results location. | | .perch/rules/ | Custom rules split across .yaml and .yml files. Commit these files. | | .perch/closed.jsonl | Dismissed findings and their reasons. Commit this file. | | perch.yaml | Custom rules. Updated by perch rules add , edit , and remove . | | .claude/ , .codex/ , .pi/ , .cursor/ | Instructions installed for the selected assistant by perch setup <assistant . | npm run check lint, typecheck, test npm run build bundle src/cli.js into dist/cli.mjs From a checkout: npm install && npm run build && npm link puts perch on the path.