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langchain-tool-builder

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Build LangChain (Python) tools using Claude Code's fail-closed design pattern — unified name/schema/security/execution in one class, with automatic three-layer execution (validate → permission → call). Use this skill whenever the user wants to define a new LangChain tool, add permission or validation logic to an existing tool, set up the ClaudeStyleTool base class in a project, or asks about "build_tool", "Claude Code style tool", "工具定义", or "langchain tool with permissions". Also trigger when the user says "create a tool for X" or "定义一个工具" in a LangChain Python project context, even without mentioning Claude Code explicitly.

skills/langchain-tool-builder/SKILL.md

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Aug 26, 2026
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# LangChain Tool Builder

Helps define LangChain (Python) tools using Claude Code's `buildTool()` pattern:
a unified class that co-locates identity, schema, security properties, and execution logic,
with fail-closed defaults so new tools are safe by default.

## Why this pattern matters

Claude Code enforces three things that vanilla LangChain tools lack:
1. **Fail-closed defaults** — `is_read_only`, `is_destructive`, `is_concurrency_safe` all default to False.
   A tool that forgets to declare its properties is conservatively treated as write-capable.
2. **Layered execution** — `validate_semantics → check_permissions → _call` are separate methods,
   so validation logic doesn't bleed into permission logic or business logic.
3. **Self-contained definition** — schema, description, security metadata, and execution all live
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