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add completions support to the prompts example (#233)
Closes #220 After this, all major features have at least a basic example.
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‎pkgs/dart_mcp/example/prompts_and_completions_client.dart

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// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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/// A client that interacts with a server that provides prompts and completions
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/// for the prompt arguments.
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library;
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import 'dart:async';
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import 'dart:io';
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import 'package:dart_mcp/client.dart';
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import 'package:dart_mcp/stdio.dart';
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void main() async {
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try {
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// Change the stdin mode so we can handle bytes one at a time, to intercept
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// the tab key for auto complete.
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stdin.echoMode = false;
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stdin.lineMode = false;
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// Create the client, which is the top level object that manages all
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// server connections.
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final client = MCPClient(
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Implementation(name: 'example dart client', version: '0.1.0'),
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);
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print('connecting to server');
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// Start the server as a separate process.
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final process = await Process.start('dart', [
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'run',
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'example/prompts_and_completions_server.dart',
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]);
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// Connect the client to the server.
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final server = client.connectServer(
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stdioChannel(input: process.stdout, output: process.stdin),
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);
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// When the server connection is closed, kill the process.
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unawaited(server.done.then((_) => process.kill()));
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print('server started');
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// Initialize the server and let it know our capabilities.
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print('initializing server');
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final initializeResult = await server.initialize(
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InitializeRequest(
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protocolVersion: ProtocolVersion.latestSupported,
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capabilities: client.capabilities,
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clientInfo: client.implementation,
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),
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);
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print('initialized: $initializeResult');
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// Ensure the server supports the prompts capability.
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if (initializeResult.capabilities.prompts == null) {
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await server.shutdown();
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throw StateError('Server doesn\'t support prompts!');
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}
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// Ensure the server supports the completions capability.
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if (initializeResult.capabilities.completions == null) {
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await server.shutdown();
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throw StateError('Server doesn\'t support completions!');
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}
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// Notify the server that we are initialized.
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server.notifyInitialized();
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print('sent initialized notification');
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// List all the available prompts from the server.
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print('Listing prompts from server');
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final promptsResult = await server.listPrompts(ListPromptsRequest());
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// Iterate each prompt and have the user fill in the arguments.
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for (final prompt in promptsResult.prompts) {
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print(
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'Found prompt ${prompt.name}, fill in the following arguments using '
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'tab to complete them:',
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);
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// For each argument, get a value from the user.
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final arguments = <String, Object?>{};
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for (var argument in prompt.arguments!) {
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stdout.write('${argument.name}: ');
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// The current user query.
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var current = '';
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// Read characters until we get an enter key.
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while (true) {
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final next = stdin.readByteSync();
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// User pressed tab, lets do an auto complete
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if (next == 9) {
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final completeResult = await server.requestCompletions(
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CompleteRequest(
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// The ref is the current prompt name.
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ref: PromptReference(name: prompt.name),
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argument: CompletionArgument(
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name: argument.name,
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value: current,
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),
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),
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);
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// Just auto-fill the first completion for this example
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if (completeResult.completion.values.isNotEmpty) {
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final firstResult = completeResult.completion.values.first;
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stdout.write(firstResult.substring(current.length));
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current = firstResult;
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}
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// If there are no completions, just do nothing.
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} else if (next == 10) {
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// Enter key, assign the argument and break the loop.
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arguments[argument.name] = current;
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stdout.writeln('');
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break;
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} else if (next == 127) {
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// Backspace keypress.
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if (current.isNotEmpty) {
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// Write a backspace followed by a space and then another
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// backspace to clear one character.
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stdout.write('\b \b');
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// Trim current by one.
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current = current.substring(0, current.length - 1);
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}
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} else {
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// A regular character, just add it to current and print it to the
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// console.
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final character = String.fromCharCode(next);
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current += character;
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stdout.write(character);
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}
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}
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}
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// Now fetch the full prompt with the arguments filled in.
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final promptResult = await server.getPrompt(
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GetPromptRequest(name: prompt.name, arguments: arguments),
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);
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final promptText = promptResult.messages
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.map((m) => (m.content as TextContent).text)
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.join('');
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// Finally, print the prompt to the user.
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print('Got full prompt `${prompt.name}`: "$promptText"');
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}
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// Shutdown the client, which will also shutdown the server connection.
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await client.shutdown();
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} finally {
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// Reset the terminal modes.
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stdin.echoMode = true;
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stdin.lineMode = true;
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}
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}

‎pkgs/dart_mcp/example/prompts_server.dart renamed to ‎pkgs/dart_mcp/example/prompts_and_completions_server.dart

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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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/// A server that implements the prompts API using the [PromptsSupport] mixin.
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/// A server that implements the prompts API using the [PromptsSupport] mixin,
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/// as well as completions for the prompt arguments with the
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/// [CompletionsSupport] mixin
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library;
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import 'dart:async';
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import 'dart:io' as io;
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import 'package:dart_mcp/server.dart';
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///
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/// This server uses the [PromptsSupport] mixin to provide prompts to the
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/// client.
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base class MCPServerWithPrompts extends MCPServer with PromptsSupport {
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///
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/// It also uses the [CompletionsSupport] mixin to provide support for auto
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/// completing prompt argument values.
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base class MCPServerWithPrompts extends MCPServer
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with PromptsSupport, CompletionsSupport {
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MCPServerWithPrompts(super.channel)
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: super.fromStreamChannel(
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implementation: Implementation(
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);
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}
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@override
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/// Handles auto completing arguments based on the known [tags] and
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/// [platforms].
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FutureOr<CompleteResult> handleComplete(CompleteRequest request) {
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// Check that this is for the expected prompt reference. Prompts are
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// referenced by their name.
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if (!request.ref.isPrompt ||
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(request.ref as PromptReference).name != runTestsPrompt.name) {
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throw ArgumentError('Unrecognized reference ${request.ref}');
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}
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// Get the candidates.
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final candidates = switch (request.argument.name) {
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'tags' => tags,
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'platforms' => platforms,
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_ =>
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throw ArgumentError('Unrecognized argument ${request.argument.name}'),
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};
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// Return the result by filtering the candidates based on a simple prefix
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// match.
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return CompleteResult(
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completion: Completion(
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values: [
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for (final candidate in candidates)
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if (candidate.startsWith(request.argument.value)) candidate,
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],
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hasMore: false,
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),
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);
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}
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/// The known tags we will autocomplete.
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static final tags = ['integration', 'unit', 'slow'];
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/// The known platforms we will auto complete.
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static final platforms = ['vm', 'chrome'];
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/// A prompt that can be used to run tests.
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///
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/// This prompt has two arguments, `tags` and `platforms`.
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final runTestsPrompt = Prompt(
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static final runTestsPrompt = Prompt(
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name: 'run_tests',
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description: 'Run your dart tests',
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arguments: [

‎pkgs/dart_mcp/example/prompts_client.dart

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