1.11.4 • Public • Published


Current Version

node Build Status codecov

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

Install with Yarn or NPM to include in your project:

yarn add --dev flow-annotation-check
# or 
npm install --save-dev flow-annotation-check

or use npx to easily run the cli commands:

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

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.

import {genSummarizedReport, genCheckFlowStatus, genValidate} from 'flow-annotation-check';

The most useful public methods are:

  • genSummarizedReport(folder: string, config: Config): Promise<Report>
  • genCheckFlowStatus(flowPath: string, filePath: string): Promise<FlowStatus>

The types involved are:

type Glob = string; // See https://github.com/isaacs/node-glob
type Config = {
  include: Array<Glob>,
  exclude: Array<Glob>,
  absolute: boolean,
type FlowStatus = 'flow' | 'flow strict' | 'flow strict-local' | 'flow weak' | 'no flow';
type Report = {
  summary: {
    flow: number,
    flowstrict: number,
    flowstrictlocal: number,
    flowweak: number,
    noflow: number,
    total: number,
  files: Array<{
    file: string,
    status: FlowStatus,

genSummarizedReport(folder, config)

If you want to check a whole project at once, then call genSummarizedReport. You can pass in the root folder, like ~/my-project/src and then a configuration object with some glob strings to find your files. genSummarizedReport 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 genCheckFlowStatus easier. Each file is tested serially in order to avoid setting really long timeouts that lock up the flow server.

import {genSummarizedReport} from 'flow-annotation-check';
    include: ['**/*.js'],
    exclude: ['**/*.coffee'],
    absolute: true,
).then((report) => {
  report.files.forEach((entry) => {
    console.log(entry.status + "\t" + entry.file);

genCheckFlowStatus(flowPath, filePath)

If you're checking one file at a time then go ahead and call genCheckFlowStatus directly. This takes a string that will be passed directly into the flow binary you specify. If flow is installed in your project, or on your system path then pass 'flow' as the first argument.

import {genCheckFlowStatus} from 'flow-annotation-check';
const file = '~/path/to/project/src/main.js';
genCheckFlowStatus('flow', file).then((status) => {
  console.log(`The status of ${file} is ${status}`);


You can use npx to run flow-annotation-check against your codebase in the terminal. It's as simple as:

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

With the default flags typed out it looks like:

$ npx flow-annotation-check \
  --level=flow \
  --flow-path flow \
  --output text \
  --list-files all \
  --include "**/*.js" \
  --exclude "+(node_modules|build|flow-typed)/**/*.js" \

Or, save your configuration inside package.json file under the flow-annotation-check field. The defaults look like this:

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

CLI flags, if included, will override package.json settings. Anything not specified as a CLI flag or inside package.json will use the default value.

The common settings to 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, json or html format.
  • --show-summary Include a summary of the data in the --output stream. Summary is never included in the junit format, and always in the json format.

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

Using multiple globs for --include and --exclude can help keep your configuration easy to understand and modify. The default setting of --exclude "+(node_modules|build|flow-typed)/**/*.js" is equivalent to:

$ npx flow-annotation-check \
  -x node_modules/**/*.js \
  -x build/**/*.js \
  -x flow-typed/**/*.js \

The full list of available commands and flags can be found by running npx flow-annotation-check -h.

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 json option prints a json file with the return value of genSummarizedReport(), the Report type described above.

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, --junit-file, --json-file or --summary-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. Try them all at once!

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 package.json settings for this repo are:

$ VERBOSE=1 flow-annotation-check
Invoking: { command: 'report',
   { validate: false,
     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',
     show_summary: false,
     list_files: 'all',
     html_file: null,
     csv_file: null,
     junit_file: null,
     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
... 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 parsing_service_js.ml 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

The --validate mode works by appending a statement that contains an invalid flow type to your files, running flow to collect expected errors, and then cleaning up. By looking at the errors reported we assert that the expected annotation aligns with what flow actually outputs.

The injected statement is:


Package Sidebar


npm i flow-annotation-check

Weekly Downloads






Unpacked Size

40.6 kB

Total Files


Last publish


  • ryan953