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)
| Rule | Description |
|---|---|
endpoint-removed | An endpoint was deleted |
method-removed | An HTTP method was removed from a path |
required-param-added | A new required parameter was added |
param-removed | An existing parameter was removed |
request-field-made-required | A request field became required |
field-type-changed | A field's type was changed |
response-field-removed | A response field was removed |
enum-value-removed | An enum value was narrowed |
auth-requirement-changed | Security schemes were modified |
response-code-removed | A response status code was removed |
Non-breaking changes (info only)
| Rule | Description |
|---|---|
endpoint-added | A new endpoint was added |
optional-param-added | A new optional parameter was added |
response-field-added | A new response field was added |
enum-value-added | An enum value was widened |
description-changed | Description or summary text changed |
deprecated | An endpoint was marked as deprecated |
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