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2.5.0 • Public • Published


Automatically run Hardhat actions when files change


npm install hardhat-watcher


yarn add hardhat-watcher

Import the plugin in your hardhat.config.js:


Or if you are using TypeScript, in your hardhat.config.ts:

import 'hardhat-watcher'


This plugin adds the watch task to Hardhat:

npx hardhat watch


This plugin extends the HardhatUserConfig's object with an optional watcher field. Every property of watcher is optional.

This is the complete type:

module.exports = {
  watcher: {
    [key: string]: { // key is the name for the watcherTask
      tasks?: (string | { command: string, params?: { [key: string] => any } })[]; // Every task of the hardhat runtime is supported (including other plugins!)
      files?: string[]; // Files, directories or glob patterns to watch for changes. (defaults to `[config.paths.sources]`, which itself defaults to the `contracts` dir)
      ignoredFiles?: string[]; // Files, directories or glob patterns that should *not* be watched.
      verbose?: boolean; // Turn on for extra logging
      clearOnStart?: boolean; // Turn on to clear the logs (of older task runs) each time before running the task
      start?: string; // Run any desirable command each time before the task runs
      runOnLaunch?: boolean; // Turn on to run tasks immediately on launch. Be aware, tasks will be run with path parameter "none".


The most basic use case, which is simply compiling your files on change, is accomplished very easily with this config:

module.exports = {
  watcher: {
    compilation: {
      tasks: ['compile'],

and subsequently running npx hardhat watch compilation

A bit more involved and showcasing the use of parameters for tasks and defining multiple watcher tasks:

module.exports = {
  watcher: {
    compilation: {
      tasks: ['compile'],
      files: ['./contracts'],
      ignoredFiles: ['**/.vscode'],
      verbose: true,
      clearOnStart: true,
      start: 'echo Running my compilation task now..',
    ci: {
      tasks: [
        { command: 'compile', params: { quiet: true } },
        { command: 'test', params: { noCompile: true, testFiles: ['testfile.ts'] } },

Run npx hardhat watch ci to clean, compile and test on every file change, or run npx hardhat watch compilation to compile.

Positional arguments

Positional arguments are provided in the same way as "normal" arguments (check out the testFiles argument in the example above, it's a positional argument). In order to find the name of a positional argument, simply run yarn hardhat <YOUR_COMMAND> --help. This is an example output for the test command:

Hardhat version 2.0.2

Usage: hardhat [GLOBAL OPTIONS] test [--no-compile] [...testFiles]


  --no-compile  Don't compile before running this task


  testFiles     An optional list of files to test (default: [])

test: Runs mocha tests

For global options help run: hardhat help

Changed file as argument

The path of the changed file can be inserted into positional arguments using the template parameter {path}. This speeds up iteration in testing, especially if using single test isolation (for example, by using it.only("test") in mocha.)


module.exports = {
  watcher: {
    test: {
      tasks: [{ command: 'test', params: { testFiles: ['{path}'] } }],
      files: ['./test/**/*'],
      verbose: true,
      clearOnStart: true,
      start: 'echo Running my test task now..',

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npm i hardhat-watcher

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