developing-genkit-tooling

name	developing-genkit-tooling
description	Best practices for authoring Genkit tooling, including CLI commands and MCP server tools. Covers naming conventions, architectural patterns, and consistency guidelines. Use when this capability is needed.
metadata	{"author":"firebase"}

Developing Genkit Tooling

Naming Conventions

Consistency in naming helps users and agents navigate the tooling.

CLI Commands

Use kebab-case with colon separators for subcommands.

• Format: noun:verb or category:action
• Examples: flow:run, eval:run, init
• Arguments: Use camelCase in code (flowName) but standard format in help text (<flowName>).

MCP Tools

Use snake_case for tool names to align with MCP standards.

• Format: verb_noun
• Examples: list_flows, run_flow, list_genkit_docs, read_genkit_docs

CLI Command Architecture

Commands are implemented in cli/src/commands/ using commander.

Runtime Interaction

Most commands require interacting with the user's project runtime. Use the runWithManager utility to handle the lifecycle of the runtime process.

import { runWithManager } from '../utils/manager-utils';

// ... command definition ...
.action(async (arg, options) => {
  await runWithManager(await findProjectRoot(), async (manager) => {
    // Interact with manager here
    const result = await manager.runAction({ key: arg });
  });
});

Output Formatting

• Logging: Use logger from @genkit-ai/tools-common/utils.
• Machine Readable: Provide options for JSON output or file writing when the command produces data.
• Streaming: If the operation supports streaming (like flow:run), provide a --stream flag and pipe output to stdout.

MCP Tool Architecture

MCP tools in cli/src/mcp/ follow two distinct patterns: Static and Runtime.

Static Tools (e.g., Docs)

These tools do not require a running Genkit project context.

• Registration: defineDocsTool(server: McpServer)
• Dependencies: Only the server instance.
• Use Case: Documentation, usage guides, global configuration.

Runtime Tools (e.g., Flows, Runtime Control)

These tools interact with a specific Genkit project's runtime.

• Registration: defineRuntimeTools(server: McpServer, options: McpToolOptions)
• Dependencies: Requires options containing manager (process manager) and projectRoot.
• Schema: MUST use getCommonSchema(options.explicitProjectRoot, ...) to ensure the tool can accept a projectRoot argument when required (e.g., in multi-project environments).

// Runtime tool definition pattern
server.registerTool(
  'my_runtime_tool',
  {
    inputSchema: getCommonSchema(options.explicitProjectRoot, {
      myArg: z.string(),
    }),
  },
  async (opts) => {
    // Resolve project root before action
    const rootOrError = resolveProjectRoot(
      options.explicitProjectRoot,
      opts,
      options.projectRoot
    );
    if (typeof rootOrError !== 'string') return rootOrError;

    // access manager via options.manager
  }
);

Error Handling

MCP tools should generally catch errors and return them as content blocks with isError: true rather than throwing exceptions, which ensures the client receives a structured error response.

try {
  // operation
} catch (err) {
  const message = err instanceof Error ? err.message : String(err);
  return {
    isError: true,
    content: [{ type: 'text', text: `Error: ${message}` }],
  };
}

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