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devtools extensions

Dart & Flutter DevTools Extensions #
Extend Dart & Flutter's developer tool suite,
Dart DevTools, with your own custom tool.
DevTools' extension framework allows you to build tools that can leverage existing frameworks
and utilities from DevTools (VM service connection, theming, shared widgets, utilities, etc.).
You can add a DevTools extension to an existing pub package, or you can create a new package
that provides a DevTools extension only. In both these scenarios, the end-user must list a
dependency on the package providing the DevTools extension in order to see the extension
in DevTools.
When DevTools detects an extension is available, either from the user's app or their IDE,
the extension will show up in its own DevTools tab. The DevTools extension's content, a
Flutter web app, is embedded in an iFrame displayed dynamically in DevTools.

What types of tools are supported? #
With the DevTools extensions framework you can build many types of tools, including:

Companion tools for existing packages
New tools that are shipped as their own package
Tools that interact with a running application
Tools that do not interact with a running application
Tools that interact with project files opened in the IDE
Planned for the future: tools that interact with the Analysis server (upvote this
issue if you want this feature sooner!)

The DevTools Extensions framework comes with out of the box features that make
distributing your extension to users seamless:

Users can use your tool from DevTools in the browser
Users can use your tool embedded directly in their IDE
Users can discover and open your tool from Dart & Flutter supported IDEs

Follow the instructions below to get started, and use the
end-to-end example
for reference.
Table of contents #

Setup your package hierarchy
Create a DevTools extension

Step 1: Setup your package hierarchy

Standalone extensions
Companion extensions

Step 2: Configure your extension
Step 3: Build your extension
Step 4: Debug your extension

Publish your package with a DevTools extension
Resources and support
Testimonies from extension authors

Supported tools #
With the DevTools extensions framework you can build many types of tools, including:

Companion tools for existing packages
New tools that are shipped as their own package
Tools that require a running application
Tools that do not require a running application

The DevTools Extensions framework comes with some out of the box features that make
distributing your extension to users seamless:

Users can use your tool from DevTools in the browser
Users can use your tool embedded directly in their IDE
Users can discover and open your tool from Dart & Flutter supported IDEs

Create a DevTools Extension #
Step 1: Setup your package hierarchy #
Standalone extensions
For a standalone extension (an extension that is not being shipped as part of an existing
pub package), it is acceptable to include your extension source code in the same package
that the extension is shipped with. This will simplify development, and since users of your
package will add a dependency on your package as a dev_dependency, the size of your
package will not affect the user's app size. Your package structure will look like this:
my_new_tool
extension/
devtools/
build/
... # pre-compiled output of the Flutter web app under lib/
config.yaml
lib/ # source code for your extension Flutter web app
src/
...
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Since the extension must be built as a Flutter web app, use flutter create to generate
the package for your DevTools extension:
flutter create --template app --platforms web my_new_tool
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Now, use the my_new_tool package to configure your extension
in the next step.
Companion extensions
For a companion extension (an extension that is shipped as part of an existing pub package),
we recommend that you place your extension source code outside of your pub package. This
will help keep your package size as small as possible, since you will want to avoid inflating
the size of user apps that depend on your package. Here is the recommended package structure:
some_pkg/ # formerly the repository root of your pub package
packages/
some_pkg/ # your pub package
extension/
devtools/
build/
... # pre-compiled output of some_pkg_devtools_extension/lib
config.yaml
some_pkg_devtools_extension/
lib/ # source code for your extension Flutter web app
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Step 2: Configure your extension #
In the Dart package that will provide the DevTools extension to users,
add a top-level extension directory:
some_pkg
extension/
lib/
...
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Under this directory, create the following structure:
extension
devtools/
build/
config.yaml
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The config.yaml file contains metadata that DevTools needs to load the extension.
name: some_pkg
issueTracker: <link_to_your_issue_tracker.com>
version: 0.0.1
materialIconCodePoint: '0xe0b1'
requiresConnection: true # optional field - defaults to true
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Copy the config.yaml file content above and paste it into the config.yaml file you just
created in your package. It is important that you use the exact file name and field names
as shown, or else your extension may fail to load in DevTools.
For each key, fill in the appropriate value for your package.

name: the package name that this DevTools extension belongs to. The value of this field
will be used in the extension page title bar. (required)

issueTracker: the url for your issue tracker. When a user clicks the “Report an issue”
link in the DevTools UI, they will be directed to this url. (required)

version: the version of your DevTools extension. This version number should evolve over
time as you ship new features for your extension. The value of this field will be used in the
extension page title bar. (required)

materialIconCodePoint: corresponds to the codepoint value of an icon from
material/icons.dart.
This icon will be used for the extension’s tab in the top-level DevTools tab bar. (required)

requiresConnection: whether the extension requires a connected Dart or Flutter app to
use. This is an optional field that will default to true if unspecified. (optional)

For the most up-to-date documentation on the config.yaml spec, see
extension_config_spec.md
Now it is time to build your extension.
Step 3: Build your extension #

Create the Flutter web app

Skip this step if you are building a standalone extension, since you already did
this when you set up your package hierarchy.

From the directory where you want your extension source code to live, run the following
command, replacing some_pkg_devtools_extension with
`<your_package_name>_devtools_extension``:
flutter create --template app --platforms web some_pkg_devtools_extension
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Add the package:devtools_extensions dependency to your extension Flutter web app.
flutter pub add devtools_extensions
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You will likely also want to add a dependency on
package:devtools_app_shared, which contains
shared services, utilities, and UI components for you to use while building your extension.
See devtools_app_shared/example
for sample usages.
flutter pub add devtools_app_shared
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Add the DevToolsExtension widget at the root of your Fluter web app.
In lib/main.dart, add the following:
import 'package:devtools_extensions/devtools_extensions.dart';
import 'package:flutter/material.dart';

void main() {
runApp(const SomePkgDevToolsExtension());
}

class SomePkgDevToolsExtension extends StatelessWidget {
const SomePkgDevToolsExtension({super.key});

@override
Widget build(BuildContext context) {
return const DevToolsExtension(
child: Placeholder(), // Build your extension here
);
}
}
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The DevToolsExtension widget automatically performs all extension initialization required
to interact with DevTools. From anywhere in your extension web app, you can access the globals:

extensionManager: a manager for interacting with DevTools or the extensions framework
serviceManager: a manager for interacting with the connected vm service, if present
dtdManager: a manager for interacting with the Dart Tooling Daemon, if present

Step 4: Debug your extension #
Use the Simulated DevTools Environment (recommended for development)
For debugging purposes, you will likely want to use the "simulated DevTools environment". This
is a simulated environment that allows you to build your extension without having to develop it
as an embedded iFrame in DevTools. Running your extension this way will wrap your extension
with an environment that simulates the DevTools-to-extension connection. It also
gives you access to hot restart and a faster development cycle.

Your DevTools extension.
The VM service URI for a test app that your DevTools extension will interact with. This app
should depend on your extension’s parent package.
Buttons to perform actions that a user may trigger from DevTools.
Logs showing the messages that will be sent between your extension and DevTools.

The simulated environment is enabled by an environment parameter use_simulated_environment.
To run your extension web app with this flag enabled, add a configuration to your launch.json
file in VS code:
{
...
"configurations": [
...
{
"name": "some_pkg_devtools_extension + simulated environment",
"cwd": "packages/some_pkg_devtools_extension",
"request": "launch",
"type": "dart",
"args": [
"--dart-define=use_simulated_environment=true"
],
},
]
}
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or launch your app from the command line with the added flag:
flutter run -d chrome --dart-define=use_simulated_environment=true
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Use a real DevTools Environment
To use a real DevTools environment, you will need to perform a series of setup steps:

Develop your extension to a point where you are ready to test your changes in a
real DevTools environment. Build your flutter web app and copy the built assets from
your_extension_web_app/build/web to your pub package's extension/devtools/build directory.
Use the build_and_copy command from package:devtools_extensions to help with this step.
cd your_extension_web_app;
flutter pub get;
dart run devtools_extensions build_and_copy --source=. --dest=../some_pkg/extension/devtools
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To ensure that your extension is setup properly for loading in DevTools, run the
validate command from package:devtools_extensions. The --package argument
should point to the root of the Dart package that this extension will be published
with.
cd your_extension_web_app;
flutter pub get;
dart run devtools_extensions validate --package=../some_pkg
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Prepare and a test environment with a dependency on your pub package that is providing the
extension.

In the Dart or Flutter project where you are adding a dependency on your package, add a
path dependency that points to your
local package source code (the package that contains the extension/devtools/ directory with
your extension's assets). Once you have done this, run pub get on the package.

If your extension requires a running application, then you'll need to run the app that
depends on your extension.
If your extension does not requires a running application, then you will need to
open the test Dart or Flutter project that depends on your package in a supported IDE
(VS Code or IntelliJ / Android Studio).

Start DevTools in one of the following ways:

If your extension requires a running app, you can open DevTools either from the URI
that was printed to command line when you ran the test app, or from the IDE where you
ran your test app.
If your extension does not require a running app, you can open your Dart or Flutter
project that depends on your package in a supported IDE (VS Code or IntelliJ / Android Studio).
Open DevTools from the IDE to see your extension in the browser.

Requires Dart SDK >= 3.5 and Flutter SDK >= 3.23

If you need local or unreleased changes from DevTools, you'll need to build and run
DevTools from source. See the DevTools CONTRIBUTING.md for a guide on how to do this.
You'll need to build DevTools with the server and the front end to test extensions - see
instructions.

Connect your test app to DevTools if it is not connected already, and you should see a tab
in the DevTools app bar for your extension. The enabled or disabled state of your extension is
managed by DevTools, which is exposed from an "Extensions" menu in DevTools, available from the
action buttons in the upper right corner of the screen.

Publish your package with a DevTools extension #
In order for a package to provide a DevTools extension to its users, it must be published with the
expected content in the your_package/extension/devtools/ directory (see the
setup instructions above).

Ensure the extension/devtools/config.yaml file exists and is configured per the
specifications above. You can run the validate command
from package:devtools_extensions to verify.
cd your_extension_web_app;
flutter pub get;
dart run devtools_extensions validate --package=path/to/pkg_providing_your_extension_assets
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Use the build_and_copy command provided by package:devtools_extensions to build
your extension and copy the output to the extension/devtools directory:
cd your_extension_web_app;
flutter pub get;
dart run devtools_extensions build_and_copy --source=. --dest=../some_pkg/extension/devtools
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Then publish your package. When running pub publish, you will see a warning if you
do not have the config.yaml file and a non-empty build directory as required.
What if I don't want the extension/devtools/build/ contents checked into source control? #
As a package author, the content that you check into your git repository is completely up to you.
If you want the contents of extension/devtools/build/ to be git ignored, then you'll just need
to ensure that the extension web app is always built and included in extension/devtools/build/
when you publish your package. To do so, add the following to a .pubignore file in the
extension/devtools/ directory:
!build
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This will ensure that, even if the extension/devtools/build directory has been been git
ignored, the directory will still be included when publishing the package on pub.
To verify the published extension contents are always up to date, consider adding a tool
script to your repo that looks something like this:
publish.sh
pushd your_extension_web_app

flutter pub get
dart run devtools_extensions build_and_copy --source=. --dest=../your_pub_package/extension/devtools

popd

pushd your_pub_package
flutter pub publish
popd
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Resources and support #
Please join the Flutter Discord server and then check out
the #devtools-extension-authors
channel to connect with other DevTools extension authors and the DevTools team.
For feature requests or bugs, please file an issue
on the DevTools Github repository.
For other documentation and guides, check out the
DevTools Extensions page on flutter.dev or
Dart and Flutter DevTools extensions,
a free article on Medium.
Testimonies from extension authors #
Several packages authors in the Dart and Flutter ecosystem have built their own DevTools
extensions to provide their users with a great developer experience.

"DevTools extensions are a neat way to save hours of debugging by showing information
that would be otherwise difficult to obtain." - Remi Rousselet,
package:provider

"By allowing developers to inspect databases and find potential issues in the familiar
DevTools environment, Drift's DevTools extension saves users a lot of time and makes the
package easier to use. Writing the extension was straightforward, and I think even simple
extensions can help users a lot." - Simon Binder, package:drift

"Our DevTools extension allows Serverpod to make our developer tooling available for more
platforms and with better integration with the Dart ecosystem. Having the tools bundled with
our Serverpod package is a huge benefit, as our users won't have to install any additional
applications." - Viktor Lidholt, package:serverpod

"Thanks to DevTools extensions we could develop a separate inspector tab for interacting
with native platform views (such as a native Android button). It allowed our Patrol users
to explore native view hierarchies without installing any additional tooling - distributed
within the Patrol package itself." - Mateusz Wojtczak & the Patrol
team, package:patrol