Firebase Debugging

Overview

This sub-skill guides systematic troubleshooting of Firebase development issues. It handles emulator problems, rules violations, function errors, auth issues, and deployment failures.

Key principles:

• Identify issue type first (emulator, rules, functions, auth, deployment)
• Use Emulator UI and Rules Playground for diagnosis
• Export emulator state before restarting
• Document issues and solutions for future reference

When This Sub-Skill Applies

• Emulators won't start or have port conflicts
• Getting Firestore rules violations (PERMISSION_DENIED)
• Cloud Functions returning errors or not executing
• Authentication not working in emulators
• Deployment fails with cryptic errors
• User says: "debug", "troubleshoot", "error", "not working", "failing"

Do not use for:

• Setting up new projects → firebase-development:project-setup
• Adding new features → firebase-development:add-feature
• Code review without specific errors → firebase-development:validate

TodoWrite Workflow

Create checklist with these 10 steps:

Step 1: Identify Issue Type

Categorize the error:

| Category | Symptoms | Keywords | |----------|----------|----------| | Emulator Won't Start | Port conflicts, initialization errors | "EADDRINUSE", "emulator failed" | | Rules Violation | Permission denied on read/write | "PERMISSION_DENIED", "insufficient" | | Function Error | HTTP 500, timeout, not executing | "function failed", "timeout" | | Auth Issue | Token errors, not authenticated | "auth failed", "invalid token" | | Deployment Failure | Deploy command fails | "deployment failed", "deploy error" |

If unclear, use AskUserQuestion to clarify issue type.

Step 2: Check Emulator Logs and Terminal

For running emulators: Watch terminal output while reproducing the issue.

For emulators that won't start:

bash
lsof -i :4000 && lsof -i :5001 && lsof -i :8080  # Check ports
kill -9 <PID>  # Kill conflicting process

For deployment errors: Check firebase-debug.log

Reference: docs/examples/emulator-workflow.md

Step 3: Open Emulator UI

bash
open http://127.0.0.1:4000

Use Emulator UI to:

• View Firestore data and structure
• Check authenticated users
• Review function invocation logs
• Search consolidated logs

Step 4: Test Rules in Playground (If Rules Issue)

In Emulator UI → Firestore → Rules Playground:

1. Select operation type (get/list/create/update/delete)
2. Specify document path
3. Set auth context (uid, custom claims)
4. Add request data for writes
5. Run simulation and review evaluation trace

Reference: docs/examples/firestore-rules-patterns.md

Step 5: Add Debug Logging (If Function Error)

Add strategic console.log statements:

• Function entry confirmation
• Input data (req.body, req.params)
• Auth context (userId, API key)
• Intermediate operation results
• Error details with stack trace

Watch terminal output while reproducing.

Reference: docs/examples/express-function-architecture.md

Step 6: Verify Auth Configuration (If Auth Issue)

Check environment variables:

bash
cat functions/.env
cat hosting/.env.local  # Should have NEXT_PUBLIC_USE_EMULATORS=true

Check emulator connection in client code and API key middleware.

Reference: docs/examples/api-key-authentication.md

Step 7: Check Deployment Config (If Deployment Failure)

bash
cat firebase-debug.log  # Full error details
cat firebase.json       # Config issues
cat .firebaserc         # Project ID
firebase target:list    # Verify targets

Test predeploy hooks locally:

bash
cd functions && npm run build

Step 8: Export Emulator State

Before making fixes:

bash
# Graceful shutdown (Ctrl+C exports automatically)
# Or manual export:
firebase emulators:export ./backup-data

Verify export: ls -la .firebase/emulator-data/

Step 9: Implement and Test Fix

Apply fix based on diagnosis, then:

bash
firebase emulators:start --import=.firebase/emulator-data

Verify:

• Original error no longer occurs
• Terminal shows success logs
• Emulator UI confirms expected behavior

Step 10: Document Issue and Solution

Create entry in docs/debugging-notes.md:

• Symptom and exact error message
• Root cause
• Solution applied
• Prevention for future

Common Issues Quick Reference

| Issue | Solution | |-------|----------| | Port conflicts | lsof -i :<port>, kill process | | Data persistence lost | Use Ctrl+C (not kill) to stop emulators | | Cold start delays | First call takes 5-10s (normal) | | Rules not reloading | Restart emulators | | Admin vs Client SDK | Admin bypasses rules, client respects them | | Missing CORS | Add app.use(cors({ origin: true })) | | Emulator connection | Set NEXT_PUBLIC_USE_EMULATORS=true | | API key prefix | Verify prefix matches actual keys |

Integration with Superpowers

If Firebase-specific tools don't reveal root cause, invoke superpowers:systematic-debugging for:

• Complex multi-service interactions
• Race conditions or timing issues
• Call stack tracing beyond Firebase layer

Pattern References

• Emulator workflow: docs/examples/emulator-workflow.md
• Rules patterns: docs/examples/firestore-rules-patterns.md
• Auth patterns: docs/examples/api-key-authentication.md
• Functions: docs/examples/express-function-architecture.md