A collection of code files and explanations to help you understand what's going on under the hood of everything interesting.
Ever wondered how a search engine finds results so fast, how programming languages understand your code, or how a compiler transforms source into something a machine can run? This repository breaks down complex systems into small, readable implementations — each one based on real-world educational resources and attributed to the original authors.
The goal is simple: read the code, understand the concept. No frameworks, no bloat — just the core ideas laid bare.
| Module | Description | Based On |
|---|---|---|
| Search Engine | A minimal search engine in Python | A search engine in 80 lines of Python |
| Language Interpreter | A Lisp interpreter written in Python | How to Write a (Lisp) Interpreter (in Python) |
| Language Compiler | A super tiny JavaScript compiler | the-super-tiny-compiler |
| Key-Value Store | A mini Redis server with RESP protocol | Building a simple Redis server with Python |
| Version Control | A mini Git with content-addressable storage | ugit: Learn Git Internals by Building Git Yourself |
| Database | A mini relational DB with B-Tree and SQL parser | DBDB: Dog Bed Database |
| Coding Agent | A mini coding agent with tool dispatch and agent loop | learn-claude-code |
| Regex Engine | A regular expression engine with Thompson's NFA | Regular Expression Matching Can Be Simple And Fast |
under-all-hoods/
├── search-engine/
│ ├── README.md
│ └── search-engine-alexmolas.py
├── language-interpreter/
│ ├── README.md
│ ├── lisp-interpreter-norvig.py
│ └── test_interpreter.py
├── language-compiler/
│ ├── README.md
│ ├── tiny-compiler.py
│ └── test_compiler.py
├── key-value-store/
│ ├── README.md
│ ├── mini-redis.py
│ └── test_redis.py
├── version-control/
│ ├── README.md
│ ├── mini-git.py
│ └── test_git.py
├── database/
│ ├── README.md
│ ├── mini-db.py
│ └── test_db.py
├── coding-agent/
│ ├── README.md
│ ├── coding-agent.py
│ └── test_coding_agent.py
├── regex-engine/
│ ├── README.md
│ ├── regex-engine.py
│ └── test_regex_engine.py
├── LICENSE
└── README.md
Each module has its own directory with:
- A README explaining the concept and crediting the original source
- A Python implementation you can read and run
Planned modules, ranked by developer interest and educational value:
| Module | Description | Key Concepts | Reference |
|---|---|---|---|
| Web Server | An HTTP server from scratch | HTTP protocol, socket programming, routing, concurrency | A Simple Web Server — 500 Lines or Less |
| Container Runtime | A Docker-like container runtime | Linux namespaces, cgroups, chroot, process isolation | Rubber Docker |
| Module | Description | Key Concepts | Reference |
|---|---|---|---|
| Shell | A Unix shell | fork/exec, pipes, I/O redirection, signal handling | Write a Shell in Python |
| DNS Resolver | A DNS resolver from scratch | DNS protocol, UDP, recursive resolution, caching | Implement DNS in a Weekend |
| Template Engine | A Jinja-like template engine | Template parsing, code generation, sandbox execution | A Template Engine — 500 Lines or Less |
| Diff Tool | A diff algorithm implementation | Myers diff algorithm, LCS, dynamic programming | The Myers Diff Algorithm |
Pick any module that interests you, read its README for context, then dive into the code. Each implementation is self-contained and designed to be understood on its own.
This project is released under CC0 1.0 Universal — public domain. See individual module READMEs for attribution to original authors and sources.