`felt` stands for "Flutter Engine Local Tester". It's a cli tool that aims to make development in the Flutter web engine more productive and pleasant.
## What can `felt` do?
`felt` supports multiple commands as follows:
1.**`felt check-licenses`**: Checks that all Dart and JS source code files contain the correct license headers.
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You could also run `felt help` or `felt help <command>` to get more information about the available commands and arguments.
## How can I use `felt`?
Once you have your local copy of the engine [setup](https://github.com/flutter/flutter/wiki/Setting-up-the-Engine-development-environment), it's recommended that you add `/path/to/engine/src/flutter/lib/web_ui/dev` to your `PATH`.
Then you would be able to use the `felt` tool from anywhere:
```
felt check-licenses
```
or:
```
felt build --watch
```
If you don't want to add `felt` to your path, you can still invoke it using a relative path like `./web_ui/dev/felt <command>`
## Speeding up your builds
You can speed up your builds by using more CPU cores. Pass `-j` to specify the desired level of parallelism, like so:
## Speeding up your builds and tests
You can speed up `ninja` and `dart2js` by adding parallelism and taking advantage of more cores.
To speed up ninja pass `-j` to specify the desired level of parallelism, like so:
```
felt build [-w] -j 100
```
If you are a Google employee, you can use an internal instance of Goma to parallelize your builds. Because Goma compiles code on remote servers, this option is effective even on low-powered laptops.
By default, when compiling Dart code to JavaScript, we use 4 `dart2js` workers.
If you need to increase or reduce the number of workers, set the `BUILD_MAX_WORKERS_PER_TASK`
environment variable to the desired number.
## Running web engine tests
To run all tests on Chrome. This will run both integration tests and the unit tests:
```
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@@ -86,6 +102,7 @@ felt test test/golden_tests/engine/canvas_golden_test.dart
```
To debug a test on Chrome:
```
felt test --debug test/golden_tests/engine/canvas_golden_test.dart
```
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