Express Api Development

Overview

Use this skill to design and implement Express services with explicit middleware ordering, stable API errors, and operationally debuggable behavior.

Scope Boundaries

• Use this skill when the task matches the trigger condition described in description.
• Do not use this skill when the primary task falls outside this skill's domain.

Shared References

• Middleware ordering guidance:
  • references/express-middleware-ordering-guidance.md
• Error handling guidance:
  • references/express-error-handling-guidance.md

Templates And Assets

• Route module starter:
  • assets/express-route-module-template.js
• Error catalog template:
  • assets/express-error-catalog-template.md
• Verification checklist:
  • assets/express-api-verification-checklist.md

Inputs To Gather

• Endpoint requirements and validation rules.
• AuthN/AuthZ and rate-limit requirements.
• Logging and observability expectations.
• Existing middleware stack and error contract conventions.
• Request/response shape contracts for boundary-safe handoff to service layer.

Deliverables

• Route and middleware composition plan.
• Validation and error response contract.
• Security and observability integration plan.
• Verification checklist with critical-path coverage.

Workflow

1. Define route modules by domain and resource responsibility.
2. Apply middleware ordering from references/express-middleware-ordering-guidance.md.
3. Implement route handlers using assets/express-route-module-template.js.
4. Parse and validate req.params/req.query/req.body once, then map to explicit domain input objects.
5. Centralize and normalize error handling using references/express-error-handling-guidance.md and assets/express-error-catalog-template.md.
6. Validate behavior with assets/express-api-verification-checklist.md.

Quality Standard

• Middleware order is explicit, deterministic, and testable.
• Validation failures are client-actionable and consistent.
• Error responses use stable codes and correlation IDs.
• Operational signals are sufficient for incident triage.
• Route handlers do not pass raw request objects or untyped payload bags into core domain services.

Failure Conditions

• Stop when middleware side effects are order-dependent and undocumented.
• Stop when endpoints bypass centralized error mapping.
• Escalate when error contracts diverge across routes without policy approval.