Cargo Features

The core agent-client-protocol crate enables schemars by default. Existing dependencies that use the defaults retain JSON Schema generation and typed MCP tool support.

Opting out of JSON Schema generation

To use the core SDK without the schemars dependency:

[dependencies]
agent-client-protocol = { version = "2.2", default-features = false }

This disables both the SDK’s direct dependency and the schemars feature on agent-client-protocol-schema. Protocol types still support serialization and deserialization without JSON Schema generation.

Clients, agents, proxies, sessions, and custom MCP servers continue to work. Within mcp_server, the following typed tool APIs require schemars:

• McpTool
• McpToolRegistry, RegisteredMcpTool, and EnabledTools
• McpToolMetadata and McpToolSchema
• The tool_fn and tool_fn_mut functions

McpServer, McpServerConnect, McpConnectionTo, and McpConnectionContext remain available without it. MCP-over-ACP attachment still only requires its protocol feature, not JSON Schema generation.

The agent-client-protocol-rmcp integration enables schemars for its tool builders.

Unstable protocol features are independent. For example, to use draft v2 and MCP-over-ACP without JSON Schema generation:

[dependencies]
agent-client-protocol = { version = "2.2", default-features = false, features = ["unstable_protocol_v2", "unstable_mcp_over_acp"] }

To opt back in explicitly, add features = ["schemars"].