Schemaguard

SchemGuard

API Schema Drift Monitor — detect breaking changes in OpenAPI specs before they break your consumers.

Why

APIs break silently. A field gets renamed, an endpoint gets removed, an enum value disappears — and downstream consumers break in production. SchemGuard catches these before deploy.

Install

npm install -g schemaguard

Usage

Diff two specs

schemaguard diff old-api.yaml new-api.yaml

Output:

Found 11 change(s):

❌ BREAKING CHANGES (9): ────────────────────────────────────────────────── ⛔ [endpoint-removed] Endpoint removed: DELETE /pets/{petId} at: DELETE /pets/{petId}

⛔ [field-type-changed] Parameter type changed: petId (string → integer) at: GET /pets/{petId} > param petId ...

🚨 9 breaking change(s) detected — deployment blocked.

CI mode

schemaguard ci --spec ./openapi.yaml --baseline ./main-openapi.yaml

• Exit 0 = no breaking changes, safe to deploy
• Exit 1 = breaking changes detected, blocks the pipeline
• Exit 2 = error (invalid spec, file not found)

Lint a spec

schemaguard lint ./openapi.yaml

Checks for missing operationId, missing descriptions, no security schemes, etc.

JSON output

schemaguard diff old.yaml new.yaml --format json

Returns structured JSON for programmatic consumption by agents and CI tools.

What it detects

Breaking changes (exit code 1)

Non-breaking changes (info only)

GitHub Actions

- name: Check API compatibility

run: npx schemaguard ci --spec ./openapi.yaml --baseline ./baseline.yaml

Programmatic API

import { parseSpec, diffSpecs, formatDiff } from 'schemaguard';

const oldSpec = parseSpec('./v1.yaml'); const newSpec = parseSpec('./v2.yaml'); const result = diffSpecs(oldSpec, newSpec);

if (result.hasBreakingChanges) { console.log(${result.breaking.length} breaking changes found); }

License

MIT