agent-tool-builder

agent-tool-builder is a skill for Claude Code, Codex from davila7/claude-code-templates. It costs 101 tokens per session (369 once invoked), scanned A, original, MIT.

Guidance for designing the tools an AI agent uses to interact with software and external systems. It covers the rules, descriptions, examples, and error messages that guide the agent.

In plain words
What is it for?
Designing JSON schemas, writing tool descriptions and input examples, validating function-calling or MCP tools, and handling errors that an AI agent can understand.
Why use it?
Poorly described tools can make an agent choose the wrong action, fail without explanation, or waste extra processing. This helps make tool behavior clearer and easier for the agent to recover from errors.

Skill for Claude CodeCodex

About the project

Claude Code Templates is a command-line tool and catalogue for configuring Anthropic’s Claude Code with agents, commands, settings, hooks, integrations, skills, and project templates. Developers use it to browse and install reusable components for their coding workflows. The catalogue includes many of these Claude Code components.

davila7/claude-code-templates · 30,520 stars · on GitHub

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/davila7/claude-code-templates/agent-tool-builder
Any agent
npx skills add davila7/claude-code-templates --skill agent-tool-builder
Clone the repo
git clone --depth 1 https://github.com/davila7/claude-code-templates

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for agent-tool-builder

README.md
[![agentmods](https://agentmods.dev/badge/skills/davila7/claude-code-templates/agent-tool-builder.svg)](https://agentmods.dev/skills/davila7/claude-code-templates/agent-tool-builder)
Your own site
<a href="https://agentmods.dev/skills/davila7/claude-code-templates/agent-tool-builder"><img src="https://agentmods.dev/badge/skills/davila7/claude-code-templates/agent-tool-builder.svg" alt="Measured on agentmods" height="20"></a>
Per session 101 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 369 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00101 $0.00369
Opus 5 $0.00051 $0.00185
Sonnet 5 $0.00020 $0.00074
Haiku 4.5 $0.00010 $0.00037

Measured 5d ago against content hash 51b313c6bf72, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

agent-tool-builder scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 5d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

Copies of this mod

3 near-identical copies found in the catalogue:

cli-tool/components/skills/ai-research/agent-tool-builder/SKILL.md · 54 lines

What it actually says

Agent Tool Builder

You are an expert in the interface between LLMs and the outside world. You've seen tools that work beautifully and tools that cause agents to hallucinate, loop, or fail silently. The difference is almost always in the design, not the implementation.

Your core insight: The LLM never sees your code. It only sees the schema and description. A perfectly implemented tool with a vague description will fail. A simple tool with crystal-clear documentation will succeed.

You push for explicit error hand

Capabilities

  • agent-tools
  • function-calling
  • tool-schema-design
  • mcp-tools
  • tool-validation
  • tool-error-handling

Patterns

Tool Schema Design

Creating clear, unambiguous JSON Schema for tools

Tool with Input Examples

Using examples to guide LLM tool usage

Tool Error Handling

Returning errors that help the LLM recover

Anti-Patterns

❌ Vague Descriptions

❌ Silent Failures

❌ Too Many Tools

Works well with: multi-agent-orchestration, api-designer, llm-architect, backend

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 5d ago First seen · 54 lines · 101 tokens per session scan A 51b313c6bf72

Subscribe to this mod's changes

agent-tool-builder is a skill published in the GitHub repository davila7/claude-code-templates (30,520 stars, last pushed today), licensed MIT. It adds 101 tokens to every session and 369 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.