agent-tool-builder

agent-tool-builder is a skill for Claude Code, Codex from pinkpixel-dev/skills-collection-1. It costs 54 tokens per session (358 once invoked), scanned A, original, Apache-2.0.

A design guide for tools that let language models interact with software and external systems. It focuses on clear tool descriptions, input schemas, examples, validation, and useful error messages.

In plain words
What is it for?
Designing function-calling or MCP tools, writing JSON schemas, adding input examples, validating requests, and returning errors that help an agent recover.
Why use it?
It helps prevent agents from choosing the wrong tool, sending malformed inputs, looping, or failing without explanation. The guide treats the tool’s visible interface as central to reliable use.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

Good fit Designing function-calling or MCP tools, writing JSON schemas, adding input examples, validating requests, and returning errors that help an agent recover.

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Install with agentmods
npx agentmods add skills/pinkpixel-dev/skills-collection-1/agent-tool-builder
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.

Any agent
npx skills add pinkpixel-dev/skills-collection-1 --skill agent-tool-builder
Clone the repo
git clone --depth 1 https://github.com/pinkpixel-dev/skills-collection-1

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/pinkpixel-dev/skills-collection-1/agent-tool-builder/github.svg)](https://agentmods.dev/skills/pinkpixel-dev/skills-collection-1/agent-tool-builder)
Your own site
<a href="https://agentmods.dev/skills/pinkpixel-dev/skills-collection-1/agent-tool-builder"><img src="https://agentmods.dev/badge/skills/pinkpixel-dev/skills-collection-1/agent-tool-builder/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for agent-tool-builder

Your own site · 80×15
<a href="https://agentmods.dev/skills/pinkpixel-dev/skills-collection-1/agent-tool-builder"><img src="https://agentmods.dev/badge/skills/pinkpixel-dev/skills-collection-1/agent-tool-builder.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 54 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 358 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
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 5.1 $0.00054 $0.00358
Opus 5.5 $0.00022 $0.00143
Sonnet 5.5 $0.00011 $0.00072
Haiku 4.5 $0.00005 $0.00036

Measured 1mo ago against content hash a85c9bbad171, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, 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 1mo 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:

SKILLS/agent-tool-builder/SKILL.md · 59 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

When to Use

This skill is applicable to execute the workflow or actions described in the overview.

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. 1mo ago First seen · 59 lines · 54 tokens per session scan A a85c9bbad171

Subscribe to this mod's changes

agent-tool-builder is a skill published in the GitHub repository pinkpixel-dev/skills-collection-1 (9 stars, last pushed 2mo ago), licensed Apache-2.0. It adds 54 tokens to every session and 358 once invoked, about $0.0002 per session on Opus 5.5. 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 2026-08-31.

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