Skip to content


Switch branches/tags

Name already in use

A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?

Latest commit


Git stats


Failed to load latest commit information.
Latest commit message
Commit time


Build and test npm npm

A tool to selectively deploy only the Firebase Functions that changed.

functions-differ takes a list of Firebase Functions from your repository and returns a list of functions that changed since its last invocation. This helps you selectively deploy only the functions that changed, thus saving time during re-deployments.

It detects any changes to a function by bundling it into a single minified file, and calculating a hash for it. This works for changes in the function's code, changes in its installed dependencies, or any other local imports.


  • Create a .differspec.json file in the directory containing your Firebase Functions:
    ├── firebase.json
    ├── functions
        ├── src
        └── .differspec.json
  • Specify your function names and their paths in .differspec.json:

This step is optional if you use the experimental --discover flag, which lets functions-differ discover the exported Cloud Functions from your project automatically.

    "functions": {
        "login": "src/auth/login/function.ts",
        "register": "src/auth/login/function.ts"
  • Run functions-differ in the directory containing .differspec.json
cd my-firebase-project/functions
  • functions-differ will then output a list of functions that need to be (re)deployed. This includes any functions that were changed or added since its last invocation.
> functions-differ

The default output is suitable for passing to firebase deploy --only command.


functions-differ supports the following options:

Name Alias Description Default
dir d The directory containing .differspec.json file (current working directory)
write w Write output to .differspec.json file or not true
verbose v Output verbose logs false
prefix Prefix for each function name output functions:
sep Separator for each output function ,
bundlerConfig Path to the bundler config file which would be passed to esbuild
concurrency Number to control the concurrency of the bundling process. Useful in CI/CD flows with limited memory Number of functions in .differspec.json
discover (Experimental) Flag indicating whether to use automatic function path discovery true
no-discover (Experimental) Negates the --discover flag
indexFilePath (Experimental) Location of the index.ts file which exports all the functions. Optional. Only used if used with --discover src/index.ts


.differspec.json serves as persistent storage for functions-differ. It contains the following properties:

Name Description
functions JSON object containing names of functions in the repository along with their paths
hashes (AUTOGENERATED, DO NOT MODIFY) JSON object containing hashes of all functions in the functions property
lastDiff (AUTOGENERATED, DO NOT MODIFY) JSON object containing the results of the last successful invocation of functions-differ
  • The hashes and lastDiff properties are autogenerated by functions-differ, and should not be created/edited manually.


Please discuss bugs, feature requests, and help in Github Issues. Pull requests are welcome, but please make sure to open an issue for your changes first.


Install the package with npm:

npm install -g functions-differ


Automatic Functions Discovery (Experimental)

functions-differ has experimental support for discovering Cloud Functions exported from your project automatically. This lets you skip defining function paths in your .differspec.json file manually.

It does this by using the TypeScript AST on exports from your project's root index.ts file. It makes the following assumptions about your codebase:

  1. The src/index.ts file must contain all exported Cloud Functions from your project, and no other exports.
  2. Every Cloud Function is defined in a separate file. E.g.: src/auth/login/index.ts, src/auth/register/index.ts, etc.

If you use automatic functions discovery in your project, make sure the above assumptions hold true.

Integration with CI/CD

I built functions-differ to help reduce the average deployment time of Cloud Functions in a project, but does not offer native support for CI builds.

Files generated during CI builds are usually ephemeral. They are lost once the CI build completes. If you plan to run functions-differ in your CI workflow, you need to backup the .differspec.json generated by the previous build, and restore it for the next built.

Here are some ways to do that for GitHub Actions:

  1. Use caching between CI runs for the .differspec.json file.
  2. Read/store the contents of the .differspec.json file in GitHub secrets in each CI run using the gh CLI available to every job.

This tool uses ESBuild internally to bundle Cloud Functions in parallel. Bundling is a resource intensive process. If your CI builds appear to crash or run very slowly after integrating functions-differ, it could be due to high memory usage by ESBuild. Consider using the --concurrency option to control how many Cloud Functions to bundle in parallel.