# Express API Designer

> Use this when planning or refining an Express or Express-style Node.js API with route groups, middleware boundaries, validation, auth, error handling, and service layering.

- Skill: `saranskumar/express-api-designer` (Agent Skill)
- Install (CLI): `npx skillmds@latest add saranskumar/express-api-designer`
- Raw SKILL.md: https://api.skillmd.com/api/skills/saranskumar/express-api-designer/raw
- Safety review: PASS (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Integrations & APIs
- Author: saranskumar (https://skillmd.com/u/saranskumar)
- Updated: 2026-08-19
- Page: https://skillmd.com/skills/saranskumar/express-api-designer

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# Goal
Design Express APIs that are explicit about validation, auth, and service boundaries.

# When to Use
- The API uses Express or a similar middleware-based Node server.
- Route structure and handler layering need design.
- Existing middleware chains are getting messy.

# Instructions
1. Define route groups and shared middleware concerns.
2. Separate validation, auth, handlers, and domain services.
3. Define error translation and response conventions.
4. Plan tests and operational instrumentation.

# Constraints
- Do not bury business logic in middleware.
- Keep request validation explicit.
- Avoid middleware stacks that hide security-critical behavior.

# Output Format
- route map
- middleware and service layering
- validation/auth notes
- implementation guidance

# Examples
- "Design an Express API for file processing."
- "How should this middleware-heavy API be cleaned up?"