leehack/mcp_dart/mcp-dart-server

my_server/
  bin/server.dart               # Reads config, builds shared services, picks the transport.
  lib/mcp/mcp.dart              # createMcpServer(services): the only server factory.
  lib/mcp/tools/base_tool.dart  # BaseTool + registerBaseTool extension.
  lib/mcp/tools/*_tool.dart     # One class per tool; dependencies via the constructor.
  lib/mcp/resources/            # Resources and resource templates.
  lib/mcp/prompts/              # Prompts.
  lib/src/                      # Domain services and models; no mcp_dart imports.
  test/                         # In-process client/server tests.

// file: lib/src/note_repository.dart
/// Thrown when a note violates a business rule.
class NoteRejected implements Exception {
  NoteRejected(this.message);
 
  final String message;
}
 
/// Domain service; it knows nothing about MCP.
class NoteRepository {
  final Map<String, String> _notes = {};
 
  Iterable<String> get ids => _notes.keys;
 
  String? read(String id) => _notes[id];
 
  void save(String id, String text) {
    if (!RegExp(r'^[a-z0-9-]+$').hasMatch(id)) {
      throw NoteRejected('id must be lowercase letters, digits or hyphens.');
    }
    _notes[id] = text;
  }
}

// file: lib/mcp/tools/base_tool.dart
import 'package:mcp_dart/mcp_dart.dart';
 
abstract class BaseTool {
  String get name;
  String get description;
  ToolInputSchema get inputSchema;
  ToolOutputSchema? get outputSchema => null;
  ToolAnnotations? get annotations => null;
 
  Future<CallToolResult> execute(
    Map<String, dynamic> args,
    RequestHandlerExtra extra,
  );
}
 
extension ToolRegistration on McpServer {
  void registerBaseTool(BaseTool tool) {
    registerTool(
      tool.name,
      description: tool.description,
      inputSchema: tool.inputSchema,
      outputSchema: tool.outputSchema,
      annotations: tool.annotations,
      callback: tool.execute,
    );
  }
}

// file: lib/mcp/tools/add_note_tool.dart
import 'package:mcp_dart/mcp_dart.dart';
import 'package:my_server/mcp/tools/base_tool.dart';
import 'package:my_server/src/note_repository.dart';
 
class AddNoteTool extends BaseTool {
  AddNoteTool(this._notes);
 
  final NoteRepository _notes;
 
  @override
  String get name => 'add_note';
 
  @override
  String get description => 'Store a note under an id.';
 
  @override
  ToolInputSchema get inputSchema => JsonSchema.object(
        properties: {
          'id': JsonSchema.string(description: 'Lowercase note id'),
          'text': JsonSchema.string(description: 'Note body'),
        },
        required: ['id', 'text'],
      );
 
  @override
  ToolAnnotations get annotations =>
      const ToolAnnotations(idempotentHint: true);
 
  @override
  Future<CallToolResult> execute(
    Map<String, dynamic> args,
    RequestHandlerExtra extra,
  ) async {
    final id = args['id'] as String;
    try {
      _notes.save(id, args['text'] as String);
    } on NoteRejected catch (error) {
      return CallToolResult(
        isError: true,
        content: [TextContent(text: error.message)],
      );
    }
    return CallToolResult(content: [TextContent(text: 'Saved $id.')]);
  }
}

// file: lib/mcp/tools/count_notes_tool.dart
import 'package:mcp_dart/mcp_dart.dart';
import 'package:my_server/mcp/tools/base_tool.dart';
import 'package:my_server/src/note_repository.dart';
 
class CountNotesTool extends BaseTool {
  CountNotesTool(this._notes);
 
  final NoteRepository _notes;
 
  @override
  String get name => 'count_notes';
 
  @override
  String get description => 'Return how many notes are stored.';
 
  @override
  ToolInputSchema get inputSchema => JsonSchema.object(properties: {});
 
  @override
  ToolOutputSchema get outputSchema => JsonSchema.object(
        properties: {'count': JsonSchema.integer()},
        required: ['count'],
      );
 
  @override
  ToolAnnotations get annotations => const ToolAnnotations(readOnlyHint: true);
 
  @override
  Future<CallToolResult> execute(
    Map<String, dynamic> args,
    RequestHandlerExtra extra,
  ) async =>
      CallToolResult.fromStructuredContent({'count': _notes.ids.length});
}

// file: lib/mcp/resources/note_resources.dart
import 'package:mcp_dart/mcp_dart.dart';
import 'package:my_server/src/note_repository.dart';
 
void registerNoteResources(McpServer server, NoteRepository notes) {
  server.registerResource(
    'Note index',
    'notes://index',
    (description: 'All note ids', mimeType: 'text/plain'),
    (uri, extra) => ReadResourceResult(
      contents: [
        TextResourceContents(
          uri: uri.toString(),
          mimeType: 'text/plain',
          text: notes.ids.join('\n'),
        ),
      ],
    ),
  );
 
  server.registerResourceTemplate(
    'Note',
    ResourceTemplateRegistration('notes://{id}', listCallback: null),
    (description: 'One note by id', mimeType: 'text/plain'),
    (uri, variables, extra) {
      final id = variables['id'];
      final text = id is String ? notes.read(id) : null;
      if (text == null) {
        final version = extra.protocolVersion;
        throw McpError(
          version != null && isStatelessProtocolVersion(version)
              ? ErrorCode.invalidParams.value
              : ErrorCode.resourceNotFound.value,
          'Resource not found',
          {'uri': uri.toString()},
        );
      }
      return ReadResourceResult(
        contents: [
          TextResourceContents(
            uri: uri.toString(),
            mimeType: 'text/plain',
            text: text,
          ),
        ],
      );
    },
  );
}

// file: lib/mcp/prompts/note_prompts.dart
import 'package:mcp_dart/mcp_dart.dart';
import 'package:my_server/src/note_repository.dart';
 
void registerNotePrompts(McpServer server, NoteRepository notes) {
  server.registerPrompt(
    'summarize_note',
    description: 'Ask the model to summarize a note.',
    argsSchema: const {
      'id': PromptArgumentDefinition(description: 'Note id', required: true),
    },
    callback: (args, extra) {
      final id = args?['id'] as String? ?? '';
      return GetPromptResult(
        messages: [
          PromptMessage(
            role: PromptMessageRole.user,
            content: TextContent(
              text: 'Summarize this note:\n${notes.read(id) ?? '(missing)'}',
            ),
          ),
        ],
      );
    },
  );
}

// file: lib/mcp/mcp.dart
import 'package:mcp_dart/mcp_dart.dart';
import 'package:my_server/mcp/prompts/note_prompts.dart';
import 'package:my_server/mcp/resources/note_resources.dart';
import 'package:my_server/mcp/tools/add_note_tool.dart';
import 'package:my_server/mcp/tools/base_tool.dart';
import 'package:my_server/mcp/tools/count_notes_tool.dart';
import 'package:my_server/src/note_repository.dart';
 
List<BaseTool> createAllTools(NoteRepository notes) => [
      AddNoteTool(notes),
      CountNotesTool(notes),
    ];