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Verify the @flow, @flow strict and @flow weak annotations in your javascript files.

Install with NPM:

npm install flow-annotation-check

or use the global flag to easily run from bash:

npm install --global flow-annotation-check

As a library

Once installed you can import flow-annotation-check into your own module and have the checker return a list of files for you to further process.

const flowAnnotationCheck = require('flow-annotation-check');

The most useful methods are:

  • genReport(folder: string, config: Config): Promise<Array<FileReport>>
  • getStatus(filePath: string): Promise<FlowStatus>

The types involved are:

type Glob = string; // See
type Config = {
  include: Array<Glob>,
  exclude: Array<Glob>,
  absolute: boolean,
type FlowStatus = 'flow' | 'flow weak' | 'no flow';
type FileReport = {
  file: string,
  status: FlowStatus,

genReport(folder, config)

If you want to check a whole project at once, then call genReport. You can pass in the root folder, like ~/my-project/src and then a configuration object with some glob strings to find your files. genReport will return a Promise that will resolve when all matching files have had their flow-status discovered.

This is a convenience method to make working with globs and mapping over getStatus easier. Each file is tested serially in order to avoid setting really long timeouts that lock up the flow server.

    include: ['**/*.js'],
    exclude: ['**/*.coffee'],
    absolute: true,
).then((entries) => {
  entries.forEach((entry) => {
    console.log(entry.status + "\t" + entry.file);


If you're checking one file at a time then go ahead and call getStatus directly. This takes a string that will be passed directly into flow on the command line.

const file = '~/path/to/project/src/main.js';
flowAnnotationCheck.getStatus(file).then((status) => {
  console.log(`The status of ${file} is ${status}`);


If you don't want to install the package globally you can run flow-annotation-check from the CLI by adding it to your package.json file:

  "dependencies": {
    "flow-annotation-check": "^1.0.0"
  "scripts": {
    "annotations": "flow-annotation-check"

Then run that script:

npm run annotations

or if installed globally:

flow-annotation-check ~/path/to/project

The available commands and flags can be found by running flow-annotation-check -h or from the example above: npm run annotations -- --help. Click through to read the latest help output on master.

The common settings you will use are:

  • -i, --include Glob for files to include. Can be set multiple times.
  • -x, --exclude Glob for files to exclude. Can be set multiple times.
  • -a, --absolute Report absolute path names. The default is to report only filenames.
  • -o, --output Choose from either text, csv, junit, or html format.

Setting --exclude will override the defaults. So don't forget to ignore node_modules/**/*.js in addition to project specific folders.

You can also configure cli arguments directly inside your package.json file. Example:

  "dependencies": {
    "flow-annotation-check": "^1.0.0"
  "flow-annotation-check": {
    "absolute": false,
    "allow_weak": false,
    "exclude": ["+(node_modules|build|flow-typed)/**/*.js"],
    "flow_path": "flow",
    "include": ["**/*.js"],
    "output": "text",
    "list_files": "all",
    "root": "."

Output format

You can use the --output flag, or -o to set the output format of the report. All reports are printed to stdio using console.log. The --output flag has no affect when --validate is set.

The default format is text which prints a two column list of status value (one of flow, flow weak or no flow) and filename separated by the Tab character.

The csv option prints a two column list of status value and filename with each field wrapped in quotes and separated by ,.

The junit option prints an xml report suitable to be consumed by CI tools like Jenkins.

The html-table option prints an opening and closing <table> tag with two columns of data. Each row contains a data-status attribute which can be useful for styling. There is a summary of the rows inside the <tfoot> element. This does not print a full, valid, html page but it is possible to render it directly. This option, with some custom CSS, could be used as part of a dashboard where only the names of the non-flow files are listed.

In addition to the --output flag there are other flags that will return the report in different formats and save it directly to a file for you. You can set --html-file, --csv-file or --junit-file and each one will create a file containing the respective report. This is useful for getting the report in multiple formats at the same time.

For example, it is desirable for CI logs to not have any extra markup and use the default text format with the -o flag. But at the same time possible to use the --junit-file flag to feed some data into jenkins for tracking over time.


If the VERBOSE env variable is set to a truthy value then the resolved configuration params will be printed. The config is a union of defaults, values in package.json, and CLI flags. Example:

$ VERBOSE=1 flow-annotation-check
Invoking: { command: 'report',
   { absolute: false,
     allow_weak: false,
      [ 'src/__tests__/fixtures/comment-blocks-10.js',
        'src/__tests__/fixtures/no-comments.js' ],
     flow_path: 'flow',
     include: [ 'src/**/*.js' ],
     output: 'text',
     root: '/Users/ryan/Code/flow-annotation-check' } }
flow  src/__tests__/cli-test.js
flow  src/__tests__/core-test.js
flow  src/__tests__/fixtures/comment-blocks-09.flow.js
flow  src/__tests__/fixtures/comment-single-block-09.flow.js
flow  src/__tests__/fixtures/comment-single-block-10.flow.js
flow  src/__tests__/fixtures/comment-statement-09.flow.js
... snip ...

Validate mode

Flow has some internal limits on what annotations it will detect. This might mean some files might not report errors when you run flow check on the cli (see in facebook/flow). You can use the validate command to verify your existing annotations.

‼️⚠️ Save your work because --validate will modify files in your local filesystem. ⚠️‼️

flow-annotation-check --validate