How to fix Emulator: No emulators to start - firebase.json missing emulator config in Firebase

FirebaseBEGINNERMEDIUMUpdated Dec 22, 2025· 119 views

The Firebase CLI cannot find emulator configuration in your firebase.json file. This happens when the emulators section is missing or incorrectly formatted, preventing local development.

Quick fix

Fixes Emulator: No emulators to start - firebase.json missing emulator config

cat firebase.json
  1. Verify firebase.json exists and check for emulators section
  2. Run firebase init emulators to configure emulators
  3. Manually add emulators configuration to firebase.json
  4. Verify the configuration and start emulators
firebase — error
cat firebase.json
Emulator: No emulators to start - firebase.json missing emulator config

What this error means

This error occurs when you run `firebase emulators:start` but the Firebase CLI cannot find any emulator configuration in your firebase.json file. The Firebase Local Emulator Suite requires an "emulators" section in firebase.json that specifies which emulators to start and their configuration settings. The Firebase CLI looks for this configuration to determine which services (Firestore, Authentication, Functions, Hosting, etc.) to emulate locally. Without this section, the CLI has no instructions on what to start, resulting in the "No emulators to start" error. This is typically a setup issue that occurs on new projects or when the firebase.json file has been manually edited without including the emulators configuration.

Typical symptoms

  • firebase emulators:start command immediately fails with "No emulators to start"
  • firebase.json file exists but contains no "emulators" section
  • firebase init completed but emulators were not configured during setup
  • Other Firebase commands work but emulator commands fail
  • No emulator UI launches when attempting to start emulators

Common causes

  1. firebase.json file is missing the "emulators" configuration section entirely
  2. firebase init was run without selecting emulators during the setup wizard
  3. firebase.json was manually created or copied without emulator configuration
  4. The emulators section exists but is empty or incorrectly formatted
  5. CLI entered a corrupted state during initialization (rare, mostly on Windows)

How to fix "Emulator: No emulators to start - firebase.json missing emulator config"

1Verify firebase.json exists and check for emulators section

First, confirm your firebase.json file exists in your project root and check if it has an "emulators" section:

bash
cat firebase.json

If the file is missing an "emulators" section, or the section is empty, this is the root cause.

2Run firebase init emulators to configure emulators

The easiest solution is to run the Firebase initialization wizard specifically for emulators:

bash
firebase init emulators

This interactive wizard will:
- Ask which emulators you want to use (Firestore, Functions, Auth, etc.)
- Let you customize ports (or use defaults)
- Automatically update your firebase.json with the correct configuration

Select the emulators you need for your project when prompted.

3Manually add emulators configuration to firebase.json

Alternatively, manually add an "emulators" section to your firebase.json file. Here's a common configuration example:

json
{
  "emulators": {
    "auth": {
      "port": 9099
    },
    "functions": {
      "port": 5001
    },
    "firestore": {
      "port": 8080
    },
    "storage": {
      "port": 9199
    },
    "hosting": {
      "port": 5000
    },
    "ui": {
      "enabled": true,
      "port": 4000
    },
    "singleProjectMode": true
  }
}

Only include the emulators you actually need. Remove sections for services you're not using.

4Verify the configuration and start emulators

After adding the configuration, verify your firebase.json is valid JSON and start the emulators:

bash
firebase emulators:start

You should see output indicating which emulators are starting and their ports. The Emulator UI should be accessible at http://localhost:4000 (or your configured port).

Advanced notes

Default Emulator Ports: If you don't specify ports, emulators use defaults: Auth (9099), Functions (5001), Firestore (8080), Realtime Database (9000), Hosting (5000), Storage (9199), Pub/Sub (8085), and UI (4000). Explicit configuration is recommended to avoid conflicts.

Windows-Specific Issues: There are documented bugs (GitHub issues #8816, #8847, #8921) where the Firebase CLI on Windows enters a corrupted state and fails to read firebase.json correctly even when properly configured. If firebase init emulators fails repeatedly on Windows, try: (1) completely removing and reinstalling firebase-tools, (2) manually creating the emulators section, or (3) using WSL2 instead of native Windows.

Using --only Flag: The firebase emulators:start --only functions,firestore command requires those specific emulators to be configured in firebase.json. If you get "No emulators to start" with --only but it works without it, check that the emulators you're targeting are actually listed in your configuration.

Single Project Mode: Setting "singleProjectMode": true allows you to use the emulators without being logged into Firebase or having an active project. This is useful for completely offline development.

Frequently asked questions

What does "Emulator: No emulators to start - firebase.json missing emulator confi" mean?
json file. json that specifies which emulators to start and their configuration settings. ) to emulate locally.
How do I fix "Emulator: No emulators to start - firebase.json missing emulator confi"?
The Firebase CLI cannot find emulator configuration in your firebase.json file. This happens when the emulators section is missing or incorrectly formatted, preventing local development.
What causes "Emulator: No emulators to start - firebase.json missing emulator confi"?
firebase.json file is missing the "emulators" configuration section entirely firebase init was run without selecting emulators during the setup wizard firebase.json was manually created or copied without emulator configuration
Is the "Emulator: No emulators to start - firebase.json missing emulator confi" error serious?
It is a medium-severity error — more of a blocker than a risk. The steps above resolve it.

Official resources & further reading