firebase-cloud-functions

name	firebase-cloud-functions
description	Complete Cloud Functions for Firebase skill — 2nd gen (Cloud Run) mandatory, idempotency, infinite loop prevention, scaling, secrets, and deployment. Use when writing or reviewing any Cloud Function.
compatibility	Requires Firebase CLI (`npm install -g firebase-tools`). 2nd gen (Cloud Run + Eventarc) is the standard. 1st gen is legacy only.

Cloud Functions for Firebase

Serverless backend functions triggered by Firebase events (Firestore, Auth, Storage, HTTP, Pub/Sub, Scheduler, etc.). 2nd gen (Cloud Run) is mandatory for all new code.

Critical Rule: 2nd Gen Only

Agent MUST use firebase-functions/v2 imports. If 1st gen syntax is detected, convert to 2nd gen. See gen_comparison.md.

References

• 1st vs 2nd Gen Comparison: gen_comparison.md
• Idempotency & Infinite Loop Prevention: idempotency.md — THE most critical reference. Read before writing any triggered function.
• Scaling, Concurrency & Cold Start: scaling.md
• Secrets & Environment Config: secrets.md
• Triggers, Deployment & Runtime: triggers_and_deployment.md
• Local Testing & Emulator Suite: local_testing.md — emulator setup, debugging, idempotency testing protocol, CI/CD integration.

Agent Pre-Function Checklist

Before generating ANY Cloud Function:

1. 2nd gen? → firebase-functions/v2 import. 1st gen = reject.
2. Trigger type? → Firestore onUpdate/onWrite = high loop risk.
3. Idempotency guards? → Event age check + before/after guard + transaction. ALL THREE for retry-enabled functions.
4. Same document write? → Guard is MANDATORY. No unconditional update() in Firestore triggers.
5. Retry enabled? → Without idempotency = REJECT the function. Never ship retry + non-idempotent.
6. Concurrency + minInstances? → HTTP: concurrency >= 200. Background: >= 80. Set minInstances to avoid cold start.
7. Secrets? → defineSecret() + Secret Manager. NEVER functions.config() (deprecated, removed March 2027).
8. Timeout/memory/CPU? → Set realistic values in options.
9. Quota risk? → Loop + retry = potential $1000s bill. Always cap with maxInstances.

Prohibitions

• Unconditional update() / set() inside Firestore onUpdate/onWrite
• retry: true without idempotency guards
• functions.config() (deprecated)
• 1st gen syntax in new code
• setTimeout / background activity after response sent