Tool System

How agents define, register, expose, and execute tools.

The Universal Tool Shape

Every agent defines tools with the same interface:

Tool {
  name: string
  description: string
  parameters: JSONSchema
  execute(params) → result
}

Agent	Type Name	Extras
Pi	`AgentTool<TParameters>`	`label`, `executionMode` (sequential/parallel)
Goose	`Tool` (rmcp)	`ToolAnnotations` (read_only, destructive, idempotent, open_world)
Grok Build	`ToolDefinition`	`ToolKind`, `ToolNamespace`, versioned descriptions
Kimi Code	`ExecutableTool`	Per-step dynamic rebuild via `buildTools()`
OpenCode/Kilocode	Effect-TS `Tool`	`ToolRegistry` service, codec-validated
Cline	`AgentTool`	`zodToJsonSchema` for schema generation
Qwen Code	Same as OpenCode	`tool-search` for dynamic MCP discovery

Tool Surface by Agent

Agent	Total Tools	Strategy
Codex	~3	Minimal: patch + plan + shell
Pi	~4-6	Core set: read, bash, edit, write + skills
Cline	~6	read_files, run_commands, search_codebase, edit_file, apply_patch, submit_and_exit
Goose	0 built-in	All via MCP extensions (platform tools: schedule only)
Grok Build	~25	Rich built-in set per toolset variant (grok_build, grok_build_hashline, grok_build_concise)
OpenCode/Kilocode	~20	read, edit, write, bash, grep, glob, ls, web-fetch, web-search, skill, todowrite, apply-patch, enterPlanMode, exitPlanMode
Kimi Code	dynamic	Tool set determined at runtime by session config
Qwen Code	~60+	Largest surface: all of OpenCode + monitor, cron, workflow, agent, team-*, artifact, notebook-edit, image-gen, lsp, tool-search, loop-wakeup, enter/exit-worktree, send-message

Tool Protocol: Where Tools Come From

Built-in only: Codex, Pi — all tools are compiled into the binary
Built-in + MCP optional: Grok Build, Qwen Code, OpenCode/Kilocode, Cline — core tools built-in, MCP extends
MCP-native: Goose — ALL tools come from extensions via MCP. No built-in coding tools.

Tool Execution: Sequential vs Parallel

Agent	Default	Control
Pi	Configurable	Per-tool `executionMode` field
Goose	Sequential	No parallel option
Grok Build	Parallel encouraged	Prompt instructs “parallelize independent calls”
Cline	Parallel encouraged	Prompt instructs “emit all independent calls now”
Qwen Code	Parallel	Standard multi-tool-call support
Codex	Parallel	`multi_tool_use.parallel`

Tool Annotations/Metadata

Goose is unique in having rich tool annotations:

#![allow(unused)]
fn main() {
ToolAnnotations {
    title: String,
    read_only: bool,
    destructive: bool,
    idempotent: bool,
    open_world: bool,
}
}

This enables the permission system to auto-classify tools without LLM calls for simple cases.

Dynamic Tool Loading

Agents that change available tools mid-session:

Kimi Code: buildTools() re-invoked before every step (tools loaded mid-turn are immediately available)
Qwen Code: tool-search lets the model discover MCP tools on demand
Goose: Extensions can be enabled/disabled mid-conversation
Grok Build: Different toolset variants (hashline vs standard) per agent definition

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