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.
npx skills add mahmoud20138/Tradecraft --skill build-your-own-xgit clone --depth 1 https://github.com/mahmoud20138/TradecraftWrote 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/skills/mahmoud20138/tradecraft/build-your-own-x)<a href="https://agentmods.dev/skills/mahmoud20138/tradecraft/build-your-own-x"><img src="https://agentmods.dev/badge/skills/mahmoud20138/tradecraft/build-your-own-x/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/skills/mahmoud20138/tradecraft/build-your-own-x"><img src="https://agentmods.dev/badge/skills/mahmoud20138/tradecraft/build-your-own-x.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 | $0.00059 | $0.01760 |
| Opus 5 | $0.00030 | $0.00880 |
| Sonnet 5 | $0.00012 | $0.00352 |
| Haiku 4.5 | $0.00006 | $0.00176 |
Grade A, and why
build-your-own-x 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 12d 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.
How it starts
The opening of the file, as written. The whole thing — 164 lines — stays where its author put it; the contents beside it link to each section on GitHub.
build-your-own-x
USE FOR:
- "build X from scratch / implement X yourself"
- "how does Docker/Git/database/web server actually work"
- "deep dive into how technology X is implemented"
- "learning compilers / interpreters / OS / networking internals"
- "implement neural network from scratch"
- "write your own shell / regex engine / search engine"
- "understand blockchain / BitTorrent internals" tags: [education, from-scratch, systems, compilers, OS, database, Docker, Git, neural-network, blockchain, web-server, shell, regex] kind: reference category: pro-code-architecture
What Is Build-Your-Own-X?
Curated repo of step-by-step tutorials for recreating popular technologies from scratch.
"What I cannot create, I do not understand." — Richard Feynman
- Repo: https://github.com/codecrafters-io/build-your-own-x
- 300+ tutorials · 30 categories · 20+ programming languages
- Stars: 330,000+ (one of the most-starred repos on GitHub)
Complete Category Reference
| # | Category | What You Build | Languages |
|---|---|---|---|
| 1 | 3D Renderer | Ray tracer, rasterizer, path tracer | C, C++, Java, JS, Python, Rust |
| 2 | AI Model | GPT, diffusion model, CLIP, NeRF | Python, C++ |
| 3 | Augmented Reality | AR overlay, marker tracking | JS, Python |
| 4 | BitTorrent Client | Peer-to-peer file sharing | Go, Haskell, JS, Python, Rust |
| 5 | Blockchain / Crypto | Bitcoin-like chain, smart contracts | Go, Haskell, Java, JS, Python, Rust |
| 6 | Bot | Chatbot, IRC bot, Slack bot | Go, Java, JS, Python |
| 7 | Command-Line Tool | CLI parser, progress bar, formatter | Go, Python, Rust |
| 8 | Database | SQL engine, key-value store, Redis clone | C, C++, Go, Java, Python, Rust |
| 9 | Docker | Container runtime, image builder | Go, Python |
| 10 | Emulator / VM | CHIP-8, NES, Game Boy emulator | C, C++, Go, Java, JS, Rust |
| 11 | Frontend Framework | React-like library, virtual DOM, JSX | JS, TS |
| 12 | Game | Tetris, chess, Minecraft clone | C, C++, Go, Java, JS, Python |
| 13 | Git | Version control from scratch | Go, Python, Haskell, Ruby |
| 14 | Memory Allocator | malloc/free implementation | C |
| 15 | Network Stack | TCP/IP stack, HTTP client | C, Go, Python |
| 16 | Neural Network | Backprop from scratch, CNN, RNN | C, C++, Java, JS, Python |
| 17 | Operating System | Bootloader, kernel, process scheduler | C, Rust |
| 18 | Physics Engine | Rigid body, collision detection | C++, JS |
| 19 | Processor | RISC-V CPU in HDL or emulation | C, Python |
| 20 | Programming Language | Interpreter, compiler, VM, LISP | C, Go, Haskell, Java, JS, Python, Rust |
| 21 | Regex Engine | NFA/DFA regex from scratch | C, Go, Java, JS, Python |
| 22 | Search Engine | Inverted index, TF-IDF, BM25 | Python, Ruby |
| 23 | Shell | Bash-like shell, job control | C, Go, Python, Rust |
| 24 | Template Engine | Jinja/Mustache-like | JS, Python |
| 25 | Text Editor | Vim-like, kilo editor | C |
| 26 | Visual Recognition | MNIST classifier, face detection | Python |
| 27 | Voxel Engine | Minecraft-style 3D world | C++ |
| 28 | Web Browser | HTML parser, CSS layout, DOM | Python, Haskell |
| 29 | Web Server | HTTP/1.1, static file server | C, Go, Java, Python, Rust |
| 30 | Distributed Systems | Kafka-like, Raft consensus, MapReduce | Go, Java, Python |
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.
- 12d ago First seen · 164 lines · 0 tokens per session scan A fac33b2182df
build-your-own-x is a skill published in the GitHub repository mahmoud20138/Tradecraft (15 stars, last pushed 4mo ago), licensed MIT. It adds 59 tokens to every session and 1,760 once invoked, about $0.0003 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.
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