What is agent-builder?

A specialized AI helper for designing and building sub-agents for Claude Code plugins.

Use it when creating an autonomous agent for code review, exploration, building, verification, or documentation.

It turns requirements into an agent with suitable triggers, configuration, process steps, and output rules.

agent-builder — Agent for Claude Code by crathgeb/claude-code-plugins

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.

Clone the repo

git clone --depth 1 https://github.com/crathgeb/claude-code-plugins

Made for: Claude Code.

Or install plugin-builder, the plugin that ships this one along with the rest of its 3 commands, 2 agents.

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.

README.md

[![agentmods](https://agentmods.dev/badge/agents/crathgeb/claude-code-plugins/agent-builder/github.svg)](https://agentmods.dev/agents/crathgeb/claude-code-plugins/agent-builder)

Your own site

<a href="https://agentmods.dev/agents/crathgeb/claude-code-plugins/agent-builder"><img src="https://agentmods.dev/badge/agents/crathgeb/claude-code-plugins/agent-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.

Your own site · 80×15

<a href="https://agentmods.dev/agents/crathgeb/claude-code-plugins/agent-builder"><img src="https://agentmods.dev/badge/agents/crathgeb/claude-code-plugins/agent-builder.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 45 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.

When invoked 2,652 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.

Model	Per session	Once invoked
Fable 5.1	$0.00045	$0.02652
Opus 5.5	$0.00018	$0.01061
Sonnet 5.5	$0.00009	$0.00530
Haiku 4.5	$0.00005	$0.00265

Measured 2mo ago against content hash 1d0d71b846fb, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

agent-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 2mo 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.

plugins/plugin-builder/agents/agent-builder.md · 342 lines

How it starts

The opening of the file, as written. The whole thing — 342 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are a Claude Code sub-agent specialist. You design and build autonomous, specialized agents following established patterns from Anthropic and the community. You create agents that trigger appropriately, operate independently, and deliver actionable results.

Core Process

1. Requirements Analysis Understand the agent's specialized task, triggering scenarios, required autonomy level, and expected output format. Identify the appropriate agent pattern (Analyzer/Explorer/Builder/Verifier/Documenter).

2. Configuration & Design Select appropriate model (sonnet/opus), color coding, and tool access. Design the complete agent process flow, output format, and quality standards. Reference similar agents from the ecosystem.

3. Implementation Generate the complete agent markdown file with precise frontmatter, clear process phases, structured output guidance, explicit triggering scenarios, and quality standards. Ensure autonomous operation.

Output Guidance

Deliver a complete, production-ready agent file that includes:

Frontmatter: Valid YAML with name, triggering-focused description, model, color, and tools (if restricted)
Agent Header: Clear specialized role and core responsibility
Core Process: 3-4 phases the agent follows autonomously
Output Guidance: Specific structure and format for agent results
Triggering Scenarios: Explicit examples of when agent should activate
Quality Standards: Criteria for excellent agent performance

Make confident configuration choices. Be specific about triggering scenarios - this is critical for proper agent activation. Design for full autonomy within the agent's specialty.

Agent Pattern Selection

Analyzer Agent - Reviews code for specific concerns:

Confidence scoring (e80% threshold)
Structured findings with file:line references
Impact assessment and recommendations
Use sonnet for most, opus for complex security/correctness
Color: yellow for warnings, red for critical issues
Examples: code-reviewer, pr-test-analyzer, silent-failure-hunter, type-design-analyzer

Read the full file on GitHub · 342 lines

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.

2mo ago First seen · 342 lines · 45 tokens per session scan A 1d0d71b846fb

Subscribe to this mod's changes

agent-builder is an agent published in the GitHub repository crathgeb/claude-code-plugins (2 stars, last pushed 1y ago), licensed MIT. It adds 45 tokens to every session and 2,652 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.

Building agents

agent-builder next to 6 agents from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
agent-buildercrathgeb/claude-code-plugins	Agent	2	1y ago	MIT	A	45	Claude Code
playwright-test-generatormicrosoft/playwright	Agent	99k	today	Apache-2.0	A	151	Claude Code
.NET-Notebook-Migration-Agentmicrosoft/ai-agents-for-beginners	Agent	79k	today	MIT	A	33	Claude Code
AVM Owner Triagegithub/awesome-copilot	Agent	41k	yesterday	MIT	A	61	Claude Code
Ultimate Transparent Thinking Beast Modegithub/awesome-copilot	Agent	41k	yesterday	MIT	A	11	Claude Code
code-revieweranthropics/claude-cookbooks	Agent	54k	3d ago	MIT	A	52	Claude Code
Pimcore Expertgithub/awesome-copilot	Agent	41k	yesterday	MIT	A	26	Claude Code