Class: AppKitMcpClient

Lightweight MCP client for Databricks-hosted MCP servers.

Uses raw fetch() with JSON-RPC 2.0 over HTTP — no @modelcontextprotocol/sdk or LangChain dependency. Supports the Streamable HTTP transport only (POST with JSON-RPC request, single JSON-RPC response). Implements exactly four methods: initialize, notifications/initialized, tools/list, tools/call. No prompts/resources/completion/sampling.

All outbound URLs are gated by an McpHostPolicy: unallowlisted hosts are rejected before the first byte is sent, and workspace credentials are only forwarded to the same-origin workspace. See mcp-host-policy.ts.

Rationale for hand-rolling JSON-RPC instead of @modelcontextprotocol/sdk: see the file-level comment at the top of this module.

Constructors

Constructor

new AppKitMcpClient(
   workspaceHost: string, 
   authenticate: () => Promise<Record<string, string>>, 
   policy: McpHostPolicy, 
   options: {
  dnsLookup?: DnsLookup;
  fetchImpl?: (input: string | URL | Request, init?: RequestInit) => Promise<Response>;
}): AppKitMcpClient;

Parameters

Returns

AppKitMcpClient

Methods

callTool()

callTool(
   qualifiedName: string, 
   args: unknown, 
   authHeaders?: Record<string, string>, 
callerSignal?: AbortSignal): Promise<string>;

Parameters

Returns

Promise<string>

canForwardWorkspaceAuth()

canForwardWorkspaceAuth(serverName: string): boolean;

Whether the named MCP server may receive workspace-scoped auth headers (e.g., an OBO bearer token from an end-user request). Callers should gate auth-forwarding decisions on this to prevent credential exfiltration to non-workspace hosts.

Parameters

Returns

boolean

close()

close(): Promise<void>;

Returns

Promise<void>

connect()

connect(endpoint: McpEndpointConfig): Promise<void>;

Parameters

Returns

Promise<void>

connectAll()

connectAll(endpoints: McpEndpointConfig[]): Promise<McpConnectAllResult>;

Connects every endpoint in parallel and returns a structured summary so callers can distinguish "all connected" from "some failed".

Returning the result instead of throwing is deliberate: one misconfigured MCP server should not take down the entire agents plugin at boot, and the agents plugin uses the summary to warn at startup with the failed-endpoint names. Errors are also logged here so a caller that ignores the return still gets per-endpoint diagnostics.

Parameters

Returns

Promise<McpConnectAllResult>

connected lists the endpoint names that initialised successfully; failed carries { name, error } for the rest.

getAllToolDefinitions()

getAllToolDefinitions(): AgentToolDefinition[];

Returns

AgentToolDefinition[]