Explain Project

Generate a comprehensive, engaging project explanation document (FOR[name].md) in the project root.

Process

1. Determine the name - Use the argument if provided (e.g., /explain-project Sarah), otherwise default to the current user's name from the system (e.g., whoami or git config). Never ask - just use a sensible default.
2. Investigate the project - Follow the research steps below.
3. Write the document - Follow the writing guide and document structure below.
4. Save - Write to FOR[name].md in the project root.
5. Open - Run open -a Typora FOR[name].md to open the finished document in Typora.

Step 1: Investigate the Project

Explore the codebase systematically. Spawn parallel subagents where possible to speed this up.

Codebase structure

IMPORTANT: Always exclude dependency and build directories when searching. Never glob or search inside node_modules/, vendor/, dist/, build/, .next/, __pycache__/, target/, .gradle/, venv/, .venv/, or similar generated directories. Use src/** or other source-specific paths rather than **/* patterns.

• List top-level files and directories (use ls, not recursive glob) to understand the project layout
• Read README.md, CLAUDE.md, package.json, Cargo.toml, pyproject.toml, Gemfile, go.mod, or equivalent to identify the project's purpose, dependencies, and tech stack
• Glob for key entry points using source-specific paths (e.g., src/**/*.ts, app/**/*.rb, lib/**/*.py - not **/*)
• Read the most important 10-15 files to understand architecture and how pieces connect

Technology choices

• Identify the core technologies, frameworks, and libraries
• Look for config files that reveal tooling decisions (bundler config, linter config, CI config, Docker files, etc.)
• Note any unusual or interesting dependency choices

Git archaeology

• git log --oneline -100 for recent history and project trajectory
• git log --all --oneline --grep="fix" --grep="bug" --grep="revert" --grep="broken" --grep="workaround" --grep="hack" -i to find bug fixes and pain points
• For the most interesting bug-fix commits, read the diff: git show <hash> --stat then git show <hash> for the actual changes
• git log --diff-filter=D --summary --oneline | head -40 to find deleted files (often reveals abandoned approaches)
• git shortlog -sn --no-merges | head -10 for contributor patterns
• Look for large commits that restructured the project (refactors, migrations)

Patterns and decisions

• Search for TODO, FIXME, HACK, WORKAROUND comments - these reveal known issues and compromises
• Look at test files to understand what the team considers important to test
• Check for environment/config patterns that reveal deployment concerns

Step 2: Write the Document

Writing style

Read references/writing-guide.md before writing.

Core principles:

• Conversational, not clinical. Write like explaining the project over coffee to a smart engineer who hasn't seen it.
• Analogies are your best friend. Abstract architecture becomes concrete when compared to familiar things.
• Show the scars. Bugs, wrong turns, "oh no" moments - these are the most valuable parts.
• Be opinionated. Say what's clever, what's janky, what you'd do differently.

Document structure

Adapt this outline to fit the project. Not every project needs every section.

# FOR [Name]: [Project Name]

## What Is This Thing?
[2-3 paragraph elevator pitch. What does it do, who is it for, why does it exist?
Frame around the problem it solves, not the technology.]

## The Big Picture
[High-level architecture. Use a mental model or analogy. Describe the request
lifecycle, command flow, or data pipeline - whatever the core loop is.
Draw the satellite view before zooming in.]

## A Tour of the Codebase
[Walk the directory structure as a narrative, not a listing. Group related pieces.
Explain WHY things are organized this way. Call out the most important files.]

## The Tech Stack (and Why)
[Don't just list technologies - explain the reasoning. What problem does each
solve? Alternatives considered? Trade-offs? Group by category.]

## How the Pieces Connect
[API contracts, data flow, event systems, shared state. The connective tissue
that's hardest to understand from reading code alone.]

## Lessons from the Trenches

### Bugs That Bit Us
[Specific bugs from git history. What happened, why it was hard to find,
how it was fixed, what the takeaway is. Mini case studies.]

### Pitfalls to Watch For
[Not bugs yet but easily could be. Fragile patterns, implicit assumptions,
leaky abstractions.]

### Things Done Well
[Good engineering worth learning from. Patterns, clever solutions, good abstractions.]

## What I'd Want to Know on Day One
[Practical advice: how to run it, test it, common workflows, where to look
when something breaks.]

Calibration

• Length: 2000-4000 words depending on project complexity.
• Depth: High-level architecture with zoomed-in detail where it matters. The 20% that gives 80% understanding.
• Audience: Senior engineer, smart but no context on this project or necessarily its stack. Don't assume domain knowledge, don't over-explain fundamentals.
• Tone: Experienced colleague walking you through the project - knowledgeable, casual, occasionally funny, never condescending.