mcp_dart

MCP (Model Context Protocol) for Dart

mcp_dart is a dual-era Dart and Flutter SDK for MCP clients, servers, and AI hosts. It implements the complete core client/server wire surface of the locked MCP 2026-07-28 specification, retains the MCP 2025-11-25 feature set, and negotiates supported earlier initialization-based specifications.

Here, core means the normative wire requirements assigned to client and server roles by the pinned final specification. It excludes optional MCP extensions, host UI behavior, an authorization-server implementation, JSON Schema external-reference resolution, and custom JSON Schema vocabularies.

[!IMPORTANT] This release is mcp_dart 2.4.2. The separately versioned stable CLI remains mcp_dart_cli 0.2.1, which requires mcp_dart ^2.4.2. Current source passes every scored requirement in the official alpha.11 MCP 2025-11-25 and 2026-07-28 client and server sets, including all 25 required 2026 authorization scenarios, plus bidirectional published TypeScript SDK 2.0.0 and Python SDK 2.1.1 interoperability.

SDK Tier 1 target

The project is pursuing MCP SDK Tier 1. Tier 1 is not yet claimed or assigned. The technical baseline is green; the remaining official audit, repository-governance, and SDK Working Group steps are tracked in the roadmap and 48-feature coverage inventory.

The public maintenance contract is documented in the contribution guide, security policy, dependency policy, and versioning policy.

Requirements

Package	Minimum Dart SDK
mcp_dart 2.4.2	3.4
mcp_dart_cli 0.2.1	3.12

SDK-only generated projects retain the SDK's Dart 3.4 minimum. CLI projects use Dart 3.12 because the CLI and its toolchain target that release.

Install Dart from dart.dev.

Installation

Production channel

Use the latest stable package for production projects:

dart pub add mcp_dart

Pin the stable SDK release

Pin the stable 2.4 line explicitly when reproducible dependency resolution is important:

dependencies:
  mcp_dart: ^2.4.2

The snippets below use the current stable SDK line. Package versions remain separate from protocol profiles: McpProtocol.stable names the SDK's default compatibility policy.

The SDK and CLI are versioned independently. The stable CLI's ^2.4.2 constraint accepts SDK versions from 2.4.2 up to, but not including, 3.0.0.

For direct SDK integration, start with the getting-started guide. The CLI below is optional and provides scaffolding, inspection, and conformance commands.

What the SDK provides

• MCP servers, clients, and host integrations with null-safe Dart APIs.
• Core tools, resources, prompts, completion, elicitation, subscriptions, logging, roots, and sampling APIs with behavior selected for the negotiated protocol era. MCP 2026-07-28 logging is retained for compatibility but is deprecated upstream.
• Stdio, Streamable HTTP, IO stream, and custom transports.
• OAuth client discovery/PKCE hooks, server authentication callbacks, DNS rebinding protection, and strict Streamable HTTP validation.
• An experimental Tasks extension implementation, MCP Apps metadata helpers, and generic extension negotiation. Extensions are separate from core protocol coverage; Tasks is not an official extension or part of the SDK's core conformance claim.
• Automated MCP 2025-11-25 and MCP 2026-07-28 conformance, bidirectional published TypeScript SDK 2.0.0 interoperability, bidirectional Python SDK 2.1.1 interoperability, real-browser transport tests, a real Flutter Web service integration in Chrome, deterministic widget tests, and an independent pinned JSON Schema Test Suite gate.
• mcp_dart 2.4.2 bounds incoming stdio and IO stream messages to 10 MiB by default, with configurable limits for larger messages. See the transport guide before upgrading integrations that exchange larger frames.
• Hardened Streamable HTTP access and JSON-RPC error diagnostics, plus the deprecated, opt-in legacy HTTP+SSE client with same-origin routing and bidirectional interoperability against official TypeScript SDK 1.30.0 and Python SDK 2.1.1 peers.

MCP has three roles: a host owns the user experience, a client connects that host to one server, and a server exposes tools, resources, and prompts. A host can manage multiple clients and servers.

Protocol profiles

Profile	Protocol behavior
McpProtocol.stable	Default dual-era profile: prefer MCP 2026-07-28, then fall back to initialization-based MCP specifications; body-only discovery probes are bounded to 5 seconds
McpProtocol.legacy	Initialization-era profile: negotiate the MCP 2025-11-25, MCP 2025-06-18, MCP 2025-03-26, MCP 2024-11-05, or MCP 2024-10-07 specification
McpProtocol.require2026	Require MCP 2026-07-28 and reject legacy initialization

Use stableProtocolVersion or defaultProtocolVersion for MCP 2026-07-28. previewProtocolVersion remains as a deprecated alias for applications built against a 2.3 prerelease. latestInitializationProtocolVersion remains 2025-11-25 when the default profile falls back to the legacy lifecycle. For compatibility, latestProtocolVersion and supportedProtocolVersions retain their mcp_dart 2.2 initialization-era values; use allSupportedProtocolVersions for the dual-era list.

Select a profile only when you need to constrain negotiation:

final legacyClient = McpClient(
  const Implementation(name: 'my-client', version: '1.0.0'),
  options: const McpClientOptions(protocol: McpProtocol.legacy),
);

final strict2026Server = McpServer(
  const Implementation(name: 'my-server', version: '1.0.0'),
  options: const McpServerOptions(protocol: McpProtocol.require2026),
);

See the MCP 2026-07-28 transition guide for fallback rules and APIs specific to MCP 2026-07-28, or run the strict MCP 2026-07-28 example. Applications upgrading from the stable 2.2 line should also follow the 2.2 to 2.3 migration guide.

Quick start with the CLI

Install the matching stable CLI:

dart pub global activate mcp_dart_cli 0.2.1
mcp_dart create my_server
cd my_server
mcp_dart inspect

The 0.2.1 CLI creates a project with mcp_dart: ^2.4.2. The inspector launches the generated stdio server itself. After leaving the interactive inspector, you can run a single tool directly:

mcp_dart inspect --tool add --json-args '{"a": 1, "b": 2}'

Useful commands:

Command	Purpose
create	Scaffold a Dart MCP server using the SDK channel paired with the CLI
serve	Run a generated server over stdio or HTTP
doctor	Check project health and connectivity
inspect	Interactively use a server's capabilities
inspect-server	Produce a structured report for a live server
inspect-client	Run a stdio harness that inspects a connecting client
trace	Proxy and record a real stdio session
conformance	Run the repository's built-in protocol regression fixtures

See the CLI documentation for command options and scope.

Documentation

• Start: getting started, server guide, client guide, quick reference
• Upgrade: 2.2 to 2.3 migration guide, migration cookbooks, MCP 2026-07-28 transition guide
• Build: tools, transports, examples, MCP Apps
• Deploy: Streamable HTTP security, OAuth examples, Flutter recipes
• Verify: interop matrix, MCP 2025-11-25 coverage, MCP 2026-07-28 coverage, day-0 runbook

Standalone integration examples may declare newer Dart SDK requirements; check each example README before running it.

Authentication

StreamableHttpClientTransport supports OAuthClientProvider and optional authorization-code discovery. Servers can use authenticator or authenticationHandler and publish protected-resource metadata.

The checked-in OAuth examples store tokens in plaintext files for local learning. Production applications must use platform secure storage or an encrypted credential service. See the OAuth examples and Streamable HTTP authentication.

Do not expose example HTTP servers directly to untrusted networks. Production deployments should use TLS, authenticate requests, and configure the documented Host and Origin protections.

Platform support

Target	Stdio	Streamable HTTP	Legacy HTTP+SSE	IO/custom stream
Dart VM / desktop server	Yes	Client and server	Client and server	Yes
Browser / Flutter Web	No process spawning	Client	Client	Yes
Flutter mobile	Only app-managed native helpers	Remote client	Remote client	Yes
Flutter desktop	Local helper processes	Client and server	Client and server	Yes

Legacy HTTP+SSE is deprecated under MCP SEP-2596 and is retained only for explicit compatibility. Use Streamable HTTP for new remote integrations.

See Flutter host and client recipes for lifecycle and secure-storage guidance.

Choosing a Dart MCP package

The Dart team maintains dart_mcp in dart-lang/ai. Choose it when you prefer the Dart team's APIs. Choose mcp_dart when you need this SDK's transport, security, compatibility, extension, and inspection surface. Re-check both packages' current releases before a production decision.

Support

• Issues and bug reports
• Contribution and issue-triage policy
• Security policy
• Dependency policy
• Versioning policy
• Tier 1 roadmap
• SDK on pub.dev
• 2.4.2 API reference
• Changelog
• MCP 2026-07-28 specification
• MCP 2025-11-25 specification