self-extend

name	self-extend
description	Use when you want to evolve your own capabilities — create new tools to avoid repeating patterns, add hooks to improve your own behavior, build skills to accumulate domain knowledge, or override built-in tools to adapt to project needs. This is your self-iteration interface.

Self-Extension

Overview

You can extend your own capabilities by writing files to .mimocode/. Changes to tools, hooks, and skills take effect immediately (next turn) — no restart needed.

Creating Tools

Write to .mimocode/tools/<name>.ts:

import { tool } from "@mimo-ai/plugin"

export default tool({
  description: "What this tool does",
  args: {
    param1: tool.schema.string().describe("Parameter description"),
  },
  async execute(args, ctx) {
    // ctx.directory — project root
    // ctx.worktree — git worktree root
    // ctx.abort — AbortSignal
    return `Result: ${args.param1}`
  },
})

Multiple tools per file: use named exports instead of default.

Creating Hooks

Write to .mimocode/hooks/<name>.ts — export a Hooks object:

export default {
  "tool.execute.before": async (input, output) => {
    if (input.tool === "bash" && output.args.command?.includes("rm -rf /")) {
      output.cancel = true
      output.cancelReason = "Blocked dangerous command"
    }
  },
  "experimental.chat.system.transform": async (input, output) => {
    output.system.push("Additional instruction here.")
  },
}

Hook Events

Event	Capability
tool.execute.before	Modify args or cancel=true to block
tool.execute.after	Modify tool output
tool.definition	Modify tool description/parameters
chat.params	Modify temperature, topP, maxOutputTokens
experimental.chat.system.transform	Append to system prompt
experimental.chat.messages.transform	Modify message list sent to LLM
permission.ask	Auto-allow/deny permission requests
shell.env	Inject environment variables

Tool Override

A custom tool with the same id as a built-in replaces it:

// .mimocode/tools/bash.ts — overrides built-in bash
import { tool } from "@mimo-ai/plugin"
import { execSync } from "child_process"

export default tool({
  description: "Shell with safety checks",
  args: { command: tool.schema.string() },
  async execute(args, ctx) {
    if (args.command.includes("sudo")) return "Error: sudo not allowed"
    return execSync(args.command, { encoding: "utf-8", cwd: ctx.directory })
  },
})

Creating Skills

Write to .mimocode/skills/<name>/SKILL.md:

---
name: my-skill
description: Use when [conditions]
---
Instructions here...

File Locations

Type	Path	Hot-reload
Tools	.mimocode/tools/*.ts	next turn
Hooks	.mimocode/hooks/*.ts	next turn
Skills	.mimocode/skills/*/SKILL.md	next turn
TUI	.mimocode/tui/*.tsx	restart

When to Use What

I want to...	Use
Wrap a repeated bash/API pattern	Tool
Block or modify a tool's behavior	Hook (tool.execute.before)
Inject context into system prompt	Hook (chat.system.transform)
Accumulate domain knowledge for future use	Skill
Override how a built-in tool works	Tool (same name as builtin)
Add a custom UI panel or command	TUI plugin

Detailed API Reference

For full type signatures, all available fields, and more examples:

• See @reference/tool-api.md for Tool schema and ToolContext
• See @reference/hook-api.md for all hook events with input/output types
• See @reference/skill-api.md for SKILL.md format and frontmatter fields
• See @reference/tui-api.md for TUI plugin slots, commands, dialogs, and state

Constraints

• Tools/hooks have same permissions as bash — no privilege escalation
• Cannot modify the permission system
• Tool output truncated at 50KB / 2000 lines
• Prefer small, composable extensions over monolithic ones