firebase-emulator

name	firebase-emulator
description	Access the Firebase Emulator Suite (Firestore, Auth, Functions, Hub) via REST and Admin SDK without trial-and-error. Use this skill whenever you read/write/query/clear Firestore Emulator data, create test users or obtain ID tokens from the Auth Emulator, verify Functions triggers, seed/export emulator data, or hit unexpected 403/404 from an emulator endpoint. Consult it BEFORE curling any emulator port — it encodes the auth header and host-resolution rules that otherwise cause retries.
allowed-tools	Bash, Read, Write, Grep, Glob, AskUserQuestion

Firebase Emulator

Efficient access to the Firebase Emulator Suite. Each rule below exists because skipping it has burned a real debugging session.

Iron rules

1. Always use 127.0.0.1, never localhost, in emulator URLs. localhost can resolve to IPv6 ::1, where an unrelated service (e.g. Docker publishing *:8080) may be listening — you get confusing 404s from the wrong server, and no auth header will fix it.
2. Firestore REST always needs -H "Authorization: Bearer owner" (the literal string owner). Security rules ARE evaluated by the emulator; without the header, reads fail with 403 PERMISSION_DENIED (Null value error). owner is treated as admin and bypasses rules. OAuth access tokens are NOT accepted (invalid jwt) — only owner or an Auth-Emulator-issued ID token works.
3. To act as a signed-in user with rules evaluated, sign in via the Auth Emulator REST (accounts:signInWithPassword, any ?key= string works) and pass the returned unsigned idToken as the Bearer.
4. On any unexpected 404 or off-looking response, first verify you are talking to the emulator at all: curl -s http://127.0.0.1:<port>/ and lsof -nP -iTCP:<port> -sTCP:LISTEN. Do not iterate on headers or paths against an unverified port.
5. Discover the setup, don't assume it. Read firebase.json (emulators block) and .firebaserc (project id), or ask the Hub: curl -s http://127.0.0.1:4400/emulators lists every running emulator with its host/port. Project id matters: data is namespaced per project id, so a "missing" document may just be under a different id.
6. Never stop or restart emulators the user started unless explicitly asked — they often hold imported data and parallel work.
7. An empty collection is often not a bug — seed data may simply not contain it. Check what actually exists first with documents:listCollectionIds before investigating.

Project config

Keep project-specific knowledge in config.json next to this SKILL.md:

1. Read config.json first. If it has an entry for the current project, trust it (ports, project id, region, quirks).
2. If not, detect from firebase.json / .firebaserc / package.json scripts, then save an entry:

   {
     "projects": {
       "<repo-name>": {
         "projectId": "...",
         "ports": { "firestore": 8080, "auth": 9099, "functions": 5001, "hub": 4400 },
         "functionsRegion": "us-central1",
         "startCommand": "firebase emulators:start",
         "quirks": []
       }
     }
   }
   

3. When you discover a project-specific pitfall during work (port conflicts, required env vars, seed-data layout), append it to that project's quirks so the next session skips the rediscovery.

Common operations

Substitute PROJECT (project id) and ports. Full endpoint catalogue: references/rest-api.md.

# List documents in a collection (admin, bypasses rules)
curl -s -H "Authorization: Bearer owner" \
  "http://127.0.0.1:8080/v1/projects/PROJECT/databases/(default)/documents/users?pageSize=50"

# What collections actually exist?
curl -s -H "Authorization: Bearer owner" -X POST -H 'Content-Type: application/json' -d '{}' \
  "http://127.0.0.1:8080/v1/projects/PROJECT/databases/(default)/documents:listCollectionIds"

# Query
curl -s -H "Authorization: Bearer owner" -H 'Content-Type: application/json' \
  -d '{"structuredQuery":{"from":[{"collectionId":"users"}],"limit":5}}' \
  "http://127.0.0.1:8080/v1/projects/PROJECT/databases/(default)/documents:runQuery"

# Create/update a document (handy for firing triggers without UI)
curl -s -X PATCH -H "Authorization: Bearer owner" -H 'Content-Type: application/json' \
  -d '{"fields":{"name":{"stringValue":"smoke"}}}' \
  "http://127.0.0.1:8080/v1/projects/PROJECT/databases/(default)/documents/users/test-doc"

# Wipe all Firestore data for a project id (emulator-only endpoint; no auth header needed)
curl -s -X DELETE \
  "http://127.0.0.1:8080/emulator/v1/projects/PROJECT/databases/(default)/documents"

# Create a user and grab an ID token (rules-evaluated access / callable functions)
curl -s -X POST -H 'Content-Type: application/json' \
  -d '{"email":"[e-mail]","password":"password123","returnSecureToken":true}' \
  "http://127.0.0.1:9099/identitytoolkit.googleapis.com/v1/accounts:signUp?key=fake-api-key"

# Which emulators are running, on which ports?
curl -s http://127.0.0.1:4400/emulators

Admin SDK scripts: set FIRESTORE_EMULATOR_HOST=127.0.0.1:8080 (and/or FIREBASE_AUTH_EMULATOR_HOST=127.0.0.1:9099) — no http:// prefix — and the SDK connects to the emulator as admin. Note: some project scripts string-compare this variable (localhost:8080 vs 127.0.0.1:8080), so match the value the script expects.

When something fails

Match the symptom against references/troubleshooting.md BEFORE retrying variations — 403 (missing Bearer owner), 404 (port hijacked / wrong host), hanging emulators:start (undefined params), and other known patterns are listed with their fixes.

Notes

• demo-* project ids run fully offline and can never touch production — prefer them for throwaway tests; real project ids are fine when working with imported data.
• Prefer REST over browser UI operations for verifying triggers and state transitions — faster and immune to stale-UI issues. Confirm trigger firing via emulator logs, not UI.
• The Emulator UI defaults to port 4000 but auto-increments on conflict (4001, ...). Before giving the user a UI URL, confirm the actual port from the startup logs or the Hub (curl -s http://127.0.0.1:4400/emulators).
• Keep HTTP header values ASCII-only; non-ASCII values get mangled.