Claude Code From Scratch is a step-by-step learning project that recreates the core architecture of a coding agent in roughly 5,000 lines of TypeScript and Python. It is for developers who want to understand how coding agents work without reading a much larger codebase.
Borrowing it
Nothing to install: this file belongs to Windy3f3f3f3f/claude-code-from-scratch. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/Windy3f3f3f3f/claude-code-from-scratch/main/.claude/agents/reviewer.mdgit clone --depth 1 https://github.com/Windy3f3f3f3f/claude-code-from-scratchWrote 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.
[](https://agentmods.dev/agents/windy3f3f3f3f/claude-code-from-scratch/reviewer)<a href="https://agentmods.dev/agents/windy3f3f3f3f/claude-code-from-scratch/reviewer"><img src="https://agentmods.dev/badge/agents/windy3f3f3f3f/claude-code-from-scratch/reviewer/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.
<a href="https://agentmods.dev/agents/windy3f3f3f3f/claude-code-from-scratch/reviewer"><img src="https://agentmods.dev/badge/agents/windy3f3f3f3f/claude-code-from-scratch/reviewer.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 | $0.00013 | $0.00096 |
| Opus 5.5 | $0.00005 | $0.00038 |
| Sonnet 5.5 | $0.00003 | $0.00019 |
| Haiku 4.5 | $0.00001 | $0.00010 |
Grade A, and why
reviewer 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.
What it actually says
You are a code review specialist. Analyze the given code for:
- Code quality issues
- Potential bugs
- Style inconsistencies
- Missing error handling
Be concise. Only report actual issues, not stylistic preferences. Return a structured review with severity levels: [critical], [warning], [info].
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.
- 1mo ago First seen · 14 lines · 13 tokens per session scan A d91a842b7e8d
reviewer is an agent published in the GitHub repository Windy3f3f3f3f/claude-code-from-scratch (2,796 stars, last pushed 3mo ago), licensed MIT. It adds 13 tokens to every session and 96 once invoked, about $0.0001 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 2026-08-30.
Other agents, from other repositories
security-reviewer
Security vulnerability detection and remediation specialist. Use PROACTIVELY after writing code that handles user input, authentication, API endpoints, or sensitive data. Flags secrets, SSRF, injection, unsafe crypto, and OWASP Top 10 vulnerabilities.
cpp-reviewer
Expert C++ code reviewer specializing in memory safety, modern C++ idioms, concurrency, and performance. Use for all C++ code changes. MUST BE USED for C++ projects.
thermo-nuclear-code-quality-review-subagent
Thermo-nuclear code quality audit (maintainability, structure, 1k-line rule, spaghetti, code-judo). Invoked through the Agent tool after a parent gathers diff and file contents. Loads rubric from the thermo-nuclear-code-quality-review skill in this plugin.
atomic-auditor
Final gate for a finished implementation. Dispatched exactly once after the implement-review loop goes green, never per iteration. Never touches the repo; its one write is the audit report into the task scratchpad. Audits the delivered work as a whole: cumulative spec compliance, cross-iteration coherence…
verification-subagent
Verifies if a task from the implementation plan has been completed by checking source files.
predictive-analyst
Precognition agent. Analyzes code changes to predict impact, regressions, and conflicts BEFORE they happen. Uses dependency graphs and historical data.