Builtin Tool Authoring Guide

A builtin tool is a package the agent runtime can call. It ships five faces:

Face	Lives in	Audience
Manifest + types	src/{manifest,types,systemRole}.ts	The LLM (tool spec + system prompt)
ExecutionRuntime	src/ExecutionRuntime/	Server / desktop / any runtime caller
Executor	src/client/executor/	Frontend (wraps stores/services)
Client UI	src/client/{Inspector,Render,…}/	Chat UI
Registry wiring	packages/builtin-tools/src/*.ts + src/store/tool/slices/builtin/executors/index.ts	Framework

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Read These First

Question	Doc
Where do files live? What does each face do? Wiring?	architecture.md
How do I name the tool, design APIs, write the manifest, executor, ExecutionRuntime?	tool-design.md
How do I build Inspector / Render / Placeholder / Streaming / Intervention / Portal?	ui/

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When to Use This Skill

• Creating a new packages/builtin-tool-<name>/ package
• Adding a new API method to an existing builtin tool
• Building or restyling any of the 6 client surfaces for a tool
• Wiring a tool into the central registries
• Debugging "tool not found / API not found / render not showing / placeholder stuck" errors

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Top-Level Design Principles

1. lobe-<domain> identifier is permanent. It's stored in message history. Renames need legacy aliases kept alongside the new name (see the // Legacy aliases entries in packages/builtin-tool-local-system/src/client/Inspector/index.ts, kept after listLocalFiles/searchLocalFiles were renamed to listFiles/searchFiles). Get it right the first time.
2. ApiName is an as const object, not a TS enum. It doubles as the runtime list BaseExecutor iterates over.
3. Three result fields, three audiences:
   • content: string → the LLM reads it
   • state: Record<…> → the UI's pluginState; result-domain only, never echo all params back
   • error: { type, message, body? } → both LLM and UI; type is a stable code
4. Split execution from frontend wiring.
   • src/ExecutionRuntime/ — pure runtime, no React, no Zustand, accepts services via constructor. The default place for new logic.
   • src/client/executor/ — BaseExecutor subclass that calls ExecutionRuntime (or stores/services directly when frontend-only).
5. UI defaults to "do nothing". Inspector is required (the header strip). Render/Placeholder/Streaming/Intervention/Portal are added only when there's something specific to show — empty registries are fine.
6. Style with createStaticStyles + cssVar.* (zero-runtime). Fall back to createStyles + token only when you genuinely need runtime values. Use @lobehub/ui components, not raw antd.
7. i18n keys live in packages/locales/src/default/plugin.ts. Inspector titles must come from t('builtins.<identifier>.apiName.<api>') so something renders while args stream.
8. A failed long-running call should be continuable, not just inspectable. Example: when callSubAgent stops halfway, the user says "keep going". So the fix was an optional subAgentId on callSubAgent that appends a new instruction to the same sub-agent thread — not a new "look up that run" API the model has to remember to call before retrying from scratch. Add a new API only when a user would ask for it on its own.

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Package Layout (preferred, post-2026 convention)

packages/builtin-tool-<name>/
├── package.json
└── src/
    ├── index.ts              # exports manifest + types + systemRole + Identifier (no React, no stores)
    ├── manifest.ts           # BuiltinToolManifest with JSON Schema for every API
    ├── types.ts              # ApiName const + Params/State interfaces per API
    ├── systemRole.ts         # System prompt teaching the model when/how to use the APIs
    ├── ExecutionRuntime/     # ✅ Default home for runtime logic (server- or anywhere-callable)
    │   └── index.ts
    └── client/
        ├── index.ts          # Re-exports for the registries
        ├── executor/         # ✅ Frontend executor — extends BaseExecutor, often delegates to ExecutionRuntime
        │   └── index.ts
        ├── Inspector/        # required — header chip per API
        ├── Render/           # optional — rich result card
        ├── Placeholder/      # optional — skeleton during streaming/execution
        ├── Streaming/        # optional — live output renderer (e.g. RunCommand, WriteFile)
        ├── Intervention/     # optional — approval / edit-before-run UI
        ├── Portal/           # optional — full-screen detail view
        └── components/       # shared subcomponents used by the surfaces above

Older packages (builtin-tool-calculator, etc.) still have src/executor/ as a sibling of src/client/. That's grandfathered; don't relocate without a deliberate refactor. New packages and new APIs added to existing packages should follow the layout above.

package.json exports map:

"exports": {
  ".":                  "./src/index.ts",
  "./client":           "./src/client/index.ts",
  "./executor":         "./src/client/executor/index.ts",
  "./executionRuntime": "./src/ExecutionRuntime/index.ts"
}

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Authoring Checklist

Before opening the PR:

• Identifier follows lobe-<domain> and is stable (lives in message history).
• Every <Name>ApiName value has: a manifest api[] entry, an executor method, an Inspector, an i18n apiName.* key.
• Params interfaces match the JSON Schema; State interfaces match what the executor returns and what the UI surfaces read.
• System prompt disambiguates confusable APIs and points to batch variants.
• Runtime logic lives in ExecutionRuntime/; the client/executor/ only wires stores/services and delegates.
• Executor returns { success, content, state, error? } via a single toResult() funnel — content always non-empty (default to error.message).
• Inspector handles isArgumentsStreaming, isLoading, partialArgs, missing pluginState.
• Render returns null until it has data; only created for APIs with rich results.
• Placeholder added if the API has a perceivable execution lag (search, list, crawl).
• Streaming added for APIs that emit incremental output (run command, write file, code execution).
• Intervention added if humanIntervention is set in the manifest.
• All registry files updated (see architecture.md → Registry wiring).
• i18n keys in packages/locales/src/default/plugin.ts plus dev seeds in en-US/zh-CN.
• bunx vitest run --silent='passed-only' 'packages/builtin-tool-<name>' passes.
• bun run type-check passes.

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Reference Tools

Pick the closest neighbor and copy:

If your tool is…	Read first
Pure-compute, no UI state	packages/builtin-tool-calculator/ — ExecutionRuntime reuses executor (mathjs/nerdamer work everywhere)
CRUD over a domain entity	packages/builtin-tool-task/ — full Inspector + Render set, batch variants
Heavy UI (Inspector/Render/Placeholder/Portal)	packages/builtin-tool-web-browsing/ — search-style result UI, Portal for detail view
Desktop / filesystem with all surfaces (incl. Streaming + Intervention)	packages/builtin-tool-local-system/ — ExecutionRuntime injects an ILocalSystemService, executor calls it
Server-side pure (no client executor)	packages/builtin-tool-web-browsing/ — only ExecutionRuntime is exported; the chat client doesn't run it
Needs human approval before running	packages/builtin-tool-local-system/src/client/Intervention/ — per-API approval components