agent-builder

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

In plain words
What is it for?
Use it when creating an autonomous agent for code review, exploration, building, verification, or documentation.
Why use it?
It turns requirements into an agent with suitable triggers, configuration, process steps, and output rules.

Agent

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 agents/crathgeb/claude-code-plugins/agent-builder
Clone the repo
git clone --depth 1 https://github.com/crathgeb/claude-code-plugins
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. 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 $0.00045 $0.02652
Opus 5 $0.00023 $0.01326
Sonnet 5 $0.00009 $0.00530
Haiku 4.5 $0.00005 $0.00265

Measured yesterday against content hash 1d0d71b846fb, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, 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 yesterday.

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.

  1. yesterday 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 10mo ago), licensed MIT. It adds 45 tokens to every session and 2,652 once invoked, about $0.0002 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 2026-08-31.

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