JSON, REST, and the idea of an API contract
By the end of today you can design a coherent set of endpoints for a resource, explain what makes an API RESTful beyond using HTTP, and say why a contract matters more than any individual endpoint.
YesterdayOn Day 24 you learned the envelope. Today you learn what goes inside it and how a set of endpoints becomes something coherent.
TomorrowTomorrow you switch languages, learning enough JavaScript to read the code that consumes these APIs.
Why this matters
An API contract is a promise other people build on. The same discipline appears again as a function signature on Day 4, a tool schema on Day 78, and an MCP tool definition on Day 84.
- JSON
- REST
- API contracts
- Resource modelling
Learn it
70 minCopy this into Claude or ChatGPT. It quizzes you before it explains anything, which is deliberate. The resources under it are how you check what it told you.
Today's Master Prompt
Free · sign inA prompt written for this day alone: your level, the exact scope, what to leave out, and an instruction to quiz you before it explains anything. Paste it into Claude or ChatGPT and it teaches you today's material.
Check it against something that is not a model
An assistant can be fluent and wrong, and on a topic you met today you will not catch it. These cover the same ground and were made by people who do this for a living, so they are what you hold the explanation up against. They are other people's work and we only link to them, so judge them for yourself.
3 hand-picked resources
Free · sign inVideos, official docs and articles covering the same ground, each opened and annotated by hand. They are what you check the assistant against on a day you cannot yet catch it being wrong.
Build it
45 minDesign the full set of endpoints for a library: books, borrowers and loans. Write them as a table of method, path, purpose, success status and error statuses. Then write the JSON shape for one resource and one error, and note which changes to that shape would break an existing consumer.
Recall it
20 minAnswer out loud, reveal, then mark honestly whether you had it. That score is the only thing on this page you do not get to choose.
5 recall questions
Free · sign inQuestions you answer from memory, then grade yourself against the real answer. The score is carried into the mastery rating below it, so an honest miss cannot quietly become a tick.
Rate it
Completion and mastery are tracked separately. Be honest, because an inflated rating only means the concept resurfaces sooner.
Mastery tracking
Free · sign inRate yourself against five named criteria per concept. Completion and mastery are tracked separately, and anything you rate shakily comes back automatically on a spaced schedule.
Recap
- 01JSON has no dates and no comments; conventions fill the gap
- 02The method supplies the verb, so the path should not
- 03The contract is field names, types, nullability, statuses and error shape
- 04Adding optional fields is safe; removing or renaming is not
Your progress
Free · sign inMark days complete, pick up where you left off across devices, and watch completion and mastery diverge. Free, and the account exists only so ninety days of work cannot vanish with a cleared browser.