---
name: edge-runtime-handbook
description: Next.js Edge Runtime limits — what runs where and how to split Node-only code
tags:
  - edge
  - nextjs
  - runtime
version: 1.0.0
category: development
outcomes:
  - List of APIs unavailable on Edge in user code paths
  - Split plan for Prisma native fs crypto node APIs
  - Middleware vs edge route handler placement decision
stack:
  - next
  - typescript
last_reviewed: 2026-05-19
risk_level: low
tools_allowed: read-only
requires_user_approval: false
compatibility:
  - cursor
  - claude-code
  - skills-sh
  - generic-markdown
references:
  - references/stack-nextjs.md
  - references/skill-safety.md
---

# Instructions

Explain **Edge vs Node** runtimes in **Next.js** for the user’s code.

1. Flag imports: `fs`, native Prisma client, some `crypto` patterns, large WASM — usually **Node**.
2. **Middleware** defaults edge — keep fast; no heavy I/O.
3. **Route segment config** `runtime = 'edge' | 'nodejs'` — justify per route.
4. **Env:** `process.env` inlined on edge — secrets risk; use public env only on edge.
5. Suggest **split:** edge handler validates + forwards to Node server action or internal API if needed.

## Outcomes

- Table: file → current runtime → recommended runtime → blockers.

## Output Rules

Link to Next docs concepts by name; no fabricated API lists — say “verify against installed Next version”.

## Scope and boundaries

- **In scope:** runtime choice, import restrictions, split patterns.
- **Out of scope:** Cloudflare Workers specifics unless user deploys there.

## Safety

- Read-only; warn on secret exposure on edge.

## Troubleshooting

- **Prisma on edge:** use Data Proxy or move to Node route — state tradeoffs.

**GitHub:** https://github.com/bh611627/skillcodex/tree/main/skills/edge-runtime-handbook/SKILL.md  
**npm:** https://www.npmjs.com/package/@skillcodex/skills