N8n:public API

Public API v1

Public API v1 lives in packages/cli/src/public-api/v1/, mounted at /api/v1 with API-key auth and public error formatting via PublicApiControllerRegistry (packages/cli/src/public-api/public-api-controller.registry.ts).

Two rule tiers: invariants (never break) and team defaults (follow unless an existing public contract forces otherwise). When this skill and the code disagree on a detail, the code wins — so open the files below. That is a reason to check the code, not license to drop a team default.

Non-negotiable rules

• New endpoints are @PublicApiController classes under v1/controllers/, one *.public.controller.ts per feature. A controller is a class — never export = (the legacy tuple style; require-public-api-controller flags it).
• Public API and internal REST are separate HTTP surfaces. A public controller never calls an internal controller/endpoint; both reuse the same service.
• Controllers and handlers delegate to a service — never import a repository or Container.get(…Repository) (no-repository-in-public-api-handler).
• Input/output go through DTOs from @n8n/api-types; every JSON route declares @ApiResponse(Dto).
• Register each controller via a side-effect import in v1/controllers/index.ts (public-api-controllers.test.ts fails otherwise).
• Don't add business logic to legacy express-openapi-validator (EOV) handlers.
• Migrating a legacy endpoint must not change its public contract.

These are n8n-local-rules ESLint rules (see packages/cli/eslint.config.mjs) and can't be silenced inline (no-public-api-guardrail-disable). The off allowlist there covers pre-existing legacy files only — it's shrink-only, don't add to it.

Team defaults

• List endpoints: cursor-based pagination (internal API uses both cursor- and page-based — don't copy an internal endpoint's model).
• Pagination args are always offset and limit — on service methods, handler calls, and repository methods you add. Never skip/take (TypeORM names). Translate to skip/take only inside a repository, at the TypeORM find call. The public query string is still cursor + limit; offset is the decoded cursor field passed into the service, never a client-facing param.
• Updates: full-object PUT, not PATCH. A successful GET body should be acceptable as a PUT body for the same resource (round-trip), aside from server-managed/immutable fields.
• Strict input DTOs; output DTOs are an allowlist of public fields.
• Never return real secrets/tokens in responses or error details — mask with the resource's sentinel/placeholder (or omit). Echoing that sentinel on PUT means keep; any other value replaces. Detail: Updates and write-only secrets.
• "Test connection/config" endpoints validate the request body (test-before-save).

Architecture

Public and internal are sibling routes over one shared, HTTP-agnostic service; neither calls the other.

GET /rest/tags    → TagsController         ┐  JWT auth, internal shape
                                            ├─→ TagService
GET /api/v1/tags  → TagsPublicController   ┘  API-key auth, public DTO

Reuse the service behavior. Reuse a DTO only when public and internal contracts are intentionally identical; otherwise make a public-specific DTO that doesn't depend on a UI-oriented internal shape.

Before editing

Open these — they are the source of truth, not this skill:

• v1/controllers/ — copy structure from tags.public.controller.ts (list + cursor) or workflows.public.controller.ts (@Param + @ProjectScope), and index.ts for the barrel.
• Decorators in packages/@n8n/decorators/src/controller/: public-api-controller.ts, api-key-scope.ts, api-response.ts, api-error-response.ts, api-summary.ts, api-description.ts, api-tags.ts, route.ts, scoped.ts, args.ts, licensed.ts.
• The OpenAPI generator (reads the decorators above, no hand-written YAML needed for a controller route): v1/openapi-gen/generate.ts, v1/openapi-gen/decorator-routes.ts.
• Pagination helpers: v1/shared/services/pagination.service.ts (decodeCursor, encodeNextCursor).
• DTOs: packages/@n8n/api-types/src/dto/.
• Gating tests: v1/__tests__/public-api-controllers.test.ts, v1/__tests__/scope-parity.test.ts, v1/openapi-gen/__tests__/generated-spec-drift.test.ts.
• The internal controller for this resource and its neighboring functional tests.

Declaring a controller

A controller is a class marked @PublicApiController('/base') that injects the shared service via its constructor and delegates to it. Copy the shape from an existing controller in v1/controllers/ with the same operation type and auth model; reuse only what applies. Decorators, all from @n8n/decorators:

Authorization (easy to get wrong)

• @ApiKeyScope (what the API key is granted) and @ProjectScope/@GlobalScope (what the user may do) are independent. Use both when the model needs both.
• @ProjectScope reads req.params as-is and does not remap id — name the path param what the resolver expects (workflowId, credentialId, projectId, dataTableId, …). A generic id often fails.
• @ApiKeyScope takes a string, { anyOf: [...] }, or { allOf: [...] } — never a bare array. The scope must exist in the permissions registry (API_KEY_RESOURCES in @n8n/permissions); scope-parity.test.ts fails on an orphan scope.

DTOs

• Build the public response shape explicitly; don't return an ORM entity and lean on @ApiResponse stripping to hide fields.
• Treat the output DTO as an allowlist. Re-check nested relations, ownership fields, tokens, and encrypted values.
• An output DTO restricts which fields you return, not which values they may hold. The registry parses the handler's return value against it, so a value the schema rejects becomes a 500. Keep the schema loose enough for anything an existing row may contain.
• Build the response from the relations the route loaded, not from the entity type. TypeORM relations are opt-in, so two routes over the same entity can return different shapes.
• Make input DTOs strict so unknown/partial fields aren't silently accepted: Z.class(shape, { strict: true }).
• Secrets: never return a real secret; use the resource's sentinel/placeholder (or omit). See Updates and write-only secrets.

List endpoints (cursor pagination)

Copy the cursor flow from tags.public.controller.ts. The input DTO takes limit: publicApiPaginationSchema.limit plus cursor: z.string().optional() — pick limit off the schema, never spread the whole publicApiPaginationSchema (it also exports offset, which must never be a Public API query param). Use decodeCursor / encodeNextCursor from the shared pagination service; the cursor is opaque; return { data, nextCursor } (never a bare array) with nextCursor: null on the last page; an invalid cursor is a 400. Preserve an existing endpoint's cursor semantics as-is — but an offset param is a defect to remove, not a contract to preserve. Detail: List endpoints and cursor pagination.

Wiring checklist

1. v1/controllers/<feature>.public.controller.ts + side-effect import in v1/controllers/index.ts.
2. Public DTO in @n8n/api-types + export from the barrel (src/dto/).
3. @ApiKeyScope value exists in the permissions registry.
4. Don't hand-write the OpenAPI path or x-required-scope for a controller route — the generator (v1/openapi-gen/generate.ts) builds it from your decorators (@ApiSummary/@ApiDescription/@ApiTags/@ApiKeyScope/ @ApiResponse/@ApiErrorResponse). Run the full pnpm build and commit the regenerated handlers/<feature>/spec/paths/*.generated.yml fragment(s) and openapi.decorator-routes.generated.yml — generated-spec-drift.test.ts fails CI if they're stale. pnpm run build:data alone is not enough after touching a controller: it runs the generator against the already-compiled dist/, so a new/changed controller silently doesn't show up unless tsc ran first.
5. Add the route to packages/nodes-base/nodes/N8n/n8n-api-coverage.json.
6. Tests.

Testing

Always cover: happy path, input-validation failure, missing API-key scope, RBAC denial. Prefer covering the business path in packages/cli/test/integration/public-api/ (real HTTP + DB); mocked-service unit tests don't replace that. Add the cases that apply (cursor pages, not-found/conflict, no sensitive fields, credential keep/replace, migration contract) — see Testing matrix. Match the nearest existing tests.

More detail (reference.md)

• List endpoints and cursor pagination
• Updates and write-only secrets
• Test-before-save endpoints
• Errors
• Testing matrix
• Migrating legacy EOV endpoints
• Verifying a migration
• CI and merging