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Tools are the core unit of work in redop. Each tool becomes an MCP tool that a client can discover and call.

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The shape

app.tool("create_post", {
  description: "Create a post",
  input: z.object({
    title: z.string(),
  }),
  handler: ({ input }) => {
    return { ok: true, title: input.title };
  },
});

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Tool config fields

  • description explains what the tool does
  • input defines runtime validation and tool schema generation
  • handler contains the business logic
  • before runs after global onBeforeHandle
  • after runs before global onAfterHandle
  • annotations adds MCP tool metadata hints

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When to use tool-local hooks

Use tool-local before / after when logic is specific to one tool:
  • result-aware analytics
  • domain events
  • tool-specific audit trails
  • post-processing close to the handler
Keep framework-wide logging and aggregate analytics in global hooks instead.

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Common mistake

Do not move all logic into hooks. Your handler should still be the main place where the tool does its work.