API Debugging Labs

A hands-on troubleshooting lab series for developers learning how to debug common API issues.

Each lab contains a small broken Flask API. Learners must run the app, reproduce the error, investigate the cause and apply a fix.

Who this is for

This project is designed for:

• New backend developers
• API bootcamp students
• Developer education workshops
• DevRel/technical curriculum demos
• Instructors teaching debugging workflows

Learning goals

By the end of these labs, learners should be able to:

• Read API error messages and logs more carefully
• Use HTTP status codes to guide debugging
• Identity common configuration and environment problems
• Debug authenication, CORS, rate limiting, JSON and database issues
• Explain the difference between symptoms and root causes
• Document a clear troubleshooting process

Tech stack

• Python
• Flask
• SQLite
• Flask-CORS
• python-dotenv

Getting started

Clone the repo:

git clone https://github.com/lilvina/api-debugging-labs.git
cd api-debugging-labs

Create and activate a virtual environment:

python3 -m venv venv
source venv/bin/activate

Install dependencies:

pip3 install -r requirements.txt

Then test the endpoint with curl or Postman.

Lab Test

Lab	Topic	Primary Skill
Lab 1	401 Authentication Error	Debugging headers and API keys
Lab 2	Missing Environment Variables	Debugging configuration issues
Lab 3	Rate Limiting 429	Understanding API limits
Lab 4	Invalid JSON Responses	Debugging response formatting
Lab 5	CORS Issues	Debugging browser/API communication
Lab 6	Database Connection Failure	Debugging database setup

Sugguested learner workflow

For each lab:

1. Read the problem.md file.
2. Run the broken app.
3. Reproduce the issue.
4. Read the error message or API response.
5. Try the hints only if needed.
6. Fix the bug.
7. Compare your answer with solution-guide.md.
8. Review instructor-notes.md for teaching ideas.

Instructor use

These labs can be used as:

• A live debugging workshop
• A take-home exercise
• Pair programming practice
• API onboarding material
• A technical curriculum portfolio sample

Recommended workshop format

Time	Activity
5 min	Introduce the debugging strategy
10 min	Learners reproduce the bug
15 min	Learners investigate and fix
10 min	Group debrief
5 min	Instructor explains production relevance

Debugging checklist

Before jumping to the solution, ask:

• What status code am I getting?
• Is the request formatted correctly?
• Are headers missing?
• Are environment variables loaded?
• Is the server returning valid JSON?
• Is the database connected?
• Is this a browser-only issue or an API issue?

License

MIT