FAFO: Learn to Write Evals

Why read the long AF blog post when your coding agent can teach you and help you FAFO.

Learn evals by messing with them: inspect failures, fix bad graders, and try your own cases. The included learn-evals skill walks you through it.

Get started

git clone https://github.com/pandemicsyn/fafo.git
cd fafo

Open your coding agent in this directory and ask:

Use the learn-evals skill to teach me evals. Start with lesson 1. Let me predict the result and try the exercise before showing me the answer.

You can also use /learn-evals where supported. Ask for a hint, skip something you already know, or say “apply this to my app.”

The skill comes with the repo. Your agent can help install dependencies when you reach the first runnable example (Node 22.19+ required). If it can't find the skill, ask it to read .agents/skills/learn-evals/SKILL.md.

Want the tutor available in another project? Optionally install it with npx skills add pandemicsyn/fafo --skill learn-evals. The official vitest-evals skill adds library-specific guidance when you need it: npx skills add getsentry/vitest-evals.

Lesson 3 in progress: inspecting the repaired grader's results with a coding agent.