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Add default JSON schema validator to MCP client #26620

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Nov 21, 2025
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Add default JSON schema validator to MCP client #26620

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8 changes: 7 additions & 1 deletion src/content/docs/agents/model-context-protocol/mcp-client-api.mdx
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Expand Up @@ -75,7 +75,7 @@ async addMcpServer(
- **`callbackHost`** (string, optional) — Host for OAuth callback URL. If omitted, automatically derived from the incoming request
- **`agentsPrefix`** (string, optional) — URL prefix for OAuth callback path. Default: `"agents"`
- **`options`** (object, optional) — Connection configuration:
- **`client`** — MCP client configuration options (passed to `@modelcontextprotocol/sdk` Client constructor)
- **`client`** — MCP client configuration options (passed to `@modelcontextprotocol/sdk` Client constructor). By default, includes `CfWorkerJsonSchemaValidator` for validating tool parameters against JSON schemas.
- **`transport`** — Transport layer configuration:
- **`headers`** — Custom HTTP headers for authentication
- **`type`** — Transport type: `"sse"`, `"streamable-http"`, or `"auto"` (tries streamable-http first, falls back to sse)
Expand Down Expand Up @@ -115,6 +115,12 @@ export class MyAgent extends Agent<Env, never> {

If the MCP server requires OAuth authentication, `authUrl` will be returned for user authentication. Connections persist across requests and the Agent will automatically reconnect if the connection is lost.

:::note[Default JSON Schema Validation]

All MCP client connections automatically include JSON schema validation using `CfWorkerJsonSchemaValidator`. This ensures that tool parameters are validated against their schemas before execution, improving reliability and catching errors early. You can override this default by providing custom client options.

:::

**Related:**

- [OAuth handling guide](/agents/guides/oauth-mcp-client)
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