Technical Writing Skill

Core Principle

Write for your audience, not for yourself.

Technical documentation exists to help others understand and use your work. Good documentation:

• Answers questions before they're asked
• Shows, doesn't just tell (examples over abstract descriptions)
• Stays current (outdated docs are worse than no docs)
• Is findable (organized and searchable)

---

Documentation Types

1. README Files

Purpose: First impression and quick-start guide

Essential sections:

# Project Name

One-sentence description of what this project does.

## What It Does

2-3 sentences explaining the purpose and value.

## Quick Start

    npm install
    npm start
    # Now visit http://localhost:3000

## Installation

Detailed setup instructions.

## Usage

Common examples and use cases.

## Documentation

Link to full docs if they exist elsewhere.

## Contributing

How to contribute (if applicable).

## License

License information.

---

2. API Documentation

Purpose: How to use your API/library

Essential elements:

• Function/method signature
• Parameters with types
• Return value with type
• Examples
• Error conditions

Example:

def calculate_discount(price: float, coupon_code: str) -> float:
    """
    Calculate the discounted price based on coupon code.

    Args:
        price: Original price in USD (must be positive)
        coupon_code: Coupon code (e.g., "SAVE10", "FREESHIP")

    Returns:
        Discounted price in USD

    Raises:
        ValueError: If price is negative
        CouponError: If coupon code is invalid or expired

    Examples:
        >>> calculate_discount(100.0, "SAVE10")
        90.0

        >>> calculate_discount(50.0, "FREESHIP")
        50.0  # Doesn't affect price

    Note:
        Coupon codes are case-insensitive. Free shipping coupons
        don't affect the returned price.
    """

---

3. How-To Guides

Purpose: Step-by-step instructions for specific tasks

Structure:

# How to Deploy to Production

## Prerequisites

- Docker installed (v20+)
- AWS CLI configured
- Production credentials

## Steps

### 1. Build the Docker image

    docker build -t myapp:latest .

### 2. Tag for ECR

    docker tag myapp:latest 123456789.dkr.ecr.us-east-1.amazonaws.com/myapp:latest

### 3. Push to ECR

    docker push 123456789.dkr.ecr.us-east-1.amazonaws.com/myapp:latest

### 4. Update ECS service

    aws ecs update-service --cluster prod --service myapp --force-new-deployment

### 5. Verify deployment

    curl https://myapp.com/health
    # Should return: {"status": "healthy"}

## Troubleshooting

**Issue:** Docker build fails with "out of space"

**Solution:** Clean up old images: `docker system prune -a`

---

**Issue:** ECS deployment stuck at 50%

**Solution:** Check CloudWatch logs for errors in new tasks

---

4. Architecture Documentation

Purpose: Explain system design and decisions

Essential elements:

• System overview diagram
• Component responsibilities
• Data flow
• Key decisions and trade-offs
• Non-obvious constraints

Example:

# Authentication System Architecture

## Overview

We use JWT-based authentication with refresh tokens for stateless,
scalable authentication across microservices.

## Components

┌─────────────┐       ┌─────────────┐       ┌─────────────┐
│   Client    │──────▶│  Auth API   │──────▶│  User DB    │
└─────────────┘       └─────────────┘       └─────────────┘
      │                      │
      │ Access Token         │ Verify Token
      ▼                      ▼
┌─────────────┐       ┌─────────────┐
│Resource API │◀──────│  API Gateway│
└─────────────┘       └─────────────┘

### Auth API
- Handles login/logout
- Issues access tokens (15min TTL) and refresh tokens (7 day TTL)
- Validates credentials against User DB

### API Gateway
- Verifies JWT signatures
- Checks token expiration
- Rejects invalid/expired tokens

### Resource APIs
- Trust gateway verification
- Extract user ID from token
- No direct auth logic

## Key Decisions

**Decision:** JWT instead of session cookies

**Rationale:**
- Stateless (no session storage needed)
- Works across domains
- Mobile-friendly
- Scales horizontally

**Trade-off:** Cannot invalidate tokens before expiry
**Mitigation:** Short TTL (15min) + refresh token rotation

---

**Decision:** Separate access and refresh tokens

**Rationale:**
- Limit exposure if access token stolen (short TTL)
- Refresh token stored securely (httpOnly cookie)
- Can invalidate refresh tokens server-side

## Security Considerations

- Tokens signed with RS256 (asymmetric)
- Private key stored in AWS Secrets Manager
- Public key distributed to all services
- Refresh token rotation on use (one-time use)
- Rate limiting on auth endpoints (10 req/min per IP)

---

Writing Principles

1. Use Active Voice

❌ Passive: "The button should be clicked by the user" ✅ Active: "Click the button"

❌ Passive: "An error will be thrown if the input is invalid" ✅ Active: "The function throws an error if the input is invalid"

---

2. Be Specific and Concrete

❌ Vague: "Configure the system appropriately" ✅ Specific: "Set max_connections to 100 in config.yml"

❌ Vague: "The API might return an error" ✅ Specific: "Returns 404 if user not found, 400 if email invalid"

---

3. Show, Don't Just Tell

❌ Abstract: "The function takes a callback" ✅ Example:

// Takes a callback that receives the result
processData(data, (result) => {
    console.log(result);
});

---

4. Lead with "Why"

❌ What only: "Set NODE_ENV=production" ✅ Why + What: "Set NODE_ENV=production to disable debug logging and enable optimizations"

---

5. Anticipate Questions

Think about what users will ask:

• How do I install it?
• What are the prerequisites?
• What does this error mean?
• How do I debug this?
• What are the common pitfalls?

Answer them before they ask.

---

Code Examples

Make Examples Runnable

❌ Not runnable:

# Somewhere in your code
user = get_user()

✅ Runnable:

from myapp import get_user

# Get currently logged-in user
user = get_user()
print(f"Hello, {user.name}")

---

Show Expected Output

❌ No output:

python script.py

✅ With output:

$ python script.py
Processing 100 items...
Done! Saved to output.csv

---

Handle Errors in Examples

❌ Only happy path:

result = api.call()
print(result)

✅ With error handling:

try:
    result = api.call()
    print(f"Success: {result}")
except APIError as e:
    print(f"API call failed: {e}")
    # Handle error appropriately

---

Documentation Structure

Progressive Disclosure

Layer information by urgency:

1. Critical first — What user needs right now
2. Common next — Frequently needed info
3. Advanced last — Edge cases and deep dives

Example:

# Quick Start (Critical)

    npm install mylib
    import { doThing } from 'mylib'
    doThing()

# Common Use Cases (Common)

## Async operations
## Error handling
## Configuration

# Advanced Topics (Advanced)

## Custom plugins
## Performance tuning
## Internals (for contributors)

---

Organization Patterns

By User Journey:

1. Installation
2. Quick Start
3. Core Concepts
4. Common Tasks
5. Advanced Features
6. API Reference
7. Troubleshooting

By Feature:

1. Overview
2. Authentication
3. Data Models
4. API Endpoints
5. Webhooks
6. Error Handling

---

Documentation Maintenance

Keep Docs in Sync with Code

✅ Do:

• Update docs in the same PR as code changes
• Review docs during code review
• Add "update docs" to PR checklist

❌ Don't:

• Say "I'll update docs later" (you won't)
• Merge code without doc updates
• Let docs drift out of date

---

Version Documentation

For public APIs:

• Document breaking changes
• Keep old version docs accessible
• Provide migration guides

Example:

# Migration Guide: v1 → v2

## Breaking Changes

### Authentication

**v1:**
```python
client = MyAPI(api_key="...")

v2:

client = MyAPI(token="...")  # Renamed 'api_key' to 'token'

Why: Clarify that we accept JWT tokens, not just API keys

Migration Steps

1. Replace api_key= with token= in all MyAPI() calls
2. Test your integration
3. Update your API token in production settings

---

## Common Documentation Anti-Patterns

### 1. "It's Self-Explanatory"

❌ **Anti-pattern:** No docs because "code is self-documenting"

**Reality:** Code shows HOW. Docs explain WHY and WHAT FOR.

```python
# Code (shows HOW)
def calculate_checksum(data, algorithm='sha256'):
    return hashlib.new(algorithm, data).hexdigest()

# Docs (explain WHY and WHAT FOR)
"""
Calculate cryptographic checksum for data integrity verification.

Use this to:
- Verify file downloads weren't corrupted
- Detect unauthorized file modifications
- Generate unique content identifiers

Supports: md5, sha1, sha256, sha512
Default (sha256) provides good security/performance balance.
"""

---

2. Outdated Examples

❌ Anti-pattern: Examples that don't work with current version

Prevention:

• Test examples as part of CI
• Extract examples into runnable tests
• Review docs in every release

---

3. Missing Prerequisites

❌ Anti-pattern: "Just run the install script"

Reality: Script fails because user doesn't have Python 3.9+

✅ Fix:

## Prerequisites

- Python 3.9 or higher ([download](https://python.org))
- pip (included with Python)
- 500MB free disk space

Check your Python version:

    python --version

Should output: Python 3.9.0 or higher

---

4. No Troubleshooting Section

❌ Anti-pattern: "It should just work"

Reality: Users encounter issues and have nowhere to look

✅ Fix: Include common issues and solutions

## Troubleshooting

### "Module not found" error

**Cause:** Package not installed or wrong Python environment

**Solution:**
1. Activate your virtual environment: `source venv/bin/activate`
2. Reinstall: `pip install mypackage`
3. Verify: `pip show mypackage`

---

Quick Documentation Checklist

Before publishing docs:

• Accuracy — All code examples work
• Completeness — Answers common questions
• Clarity — Non-experts can understand
• Examples — Shows real usage, not toy examples
• Error handling — Explains what can go wrong
• Prerequisites — Lists requirements
• Current — Matches latest version
• Findable — Easy to navigate
• Maintainable — Can be updated easily

---

Integration with Other Skills

With Git Hygiene

• Update docs in same commit as code changes
• Commit message: "docs: add installation guide for Windows"

With Code Review

• Review docs as part of PR review
• Check that examples are accurate
• Verify API changes are documented

With Testing

• Test code examples in CI
• Use doctest (Python) or similar tools
• Ensure examples stay current

---

Quick Reference

README Template

# Project Name

One-sentence description.

## Quick Start

    # Install and run
    npm install
    npm start

## Features

- Feature 1
- Feature 2

## Documentation

See [docs/](docs/) for full documentation.

## License

MIT

API Doc Template

def function_name(param1: type1, param2: type2) -> return_type:
    """
    One-sentence description.

    Longer explanation if needed.

    Args:
        param1: Description
        param2: Description

    Returns:
        Description

    Raises:
        ErrorType: When this happens

    Examples:
        >>> function_name(value1, value2)
        expected_output
    """

---

Remember: Good documentation enables others to use your work without asking you questions. Write for your audience. Show examples. Keep it current. If users are asking the same questions repeatedly, that's a sign your docs need improvement.