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HTTP in Depth  ›  Lesson

HTTP Methods

HTTP Methods 12 minThe URL names a resource and the HTTP method says what to do with it, and each method promises whether it is safe and whether repeating it is harmless.

HTTP Methods

BookNook needs to list books, add a book, change a book's shelf, and remove a lost book. You could invent URLs like /getBook and /deleteBook, but HTTP already gives every request a verb. Use the verbs well and callers, caches and proxies all understand your API without reading a word of documentation.

The rule

The URL is the noun; the method is the verb.

The five methods you will use every day:

Method Meaning Body? Safe Idempotent
GET Read a resource No Yes Yes
POST Create inside a collection, or trigger an action Yes No No
PUT Replace a resource completely Yes No Yes
PATCH Change part of a resource Yes No Not guaranteed
DELETE Remove a resource Usually no No Yes

Two properties matter more than the names:

  • Safe: the request does not change anything on the server. GET must be safe, so crawlers and caches can call it freely.
  • Idempotent: sending the same request twice leaves the server in the same state as sending it once. Deleting book 42 twice still ends with book 42 gone. Posting the same new loan twice creates two loans.
GET    /v1/books/42        read book 42
PUT    /v1/books/42        replace book 42 with the body
PATCH  /v1/books/42        change only the fields in the body
DELETE /v1/books/42        remove book 42
POST   /v1/books           add a new book to the collection

Two supporting methods appear in the background: HEAD is a GET without the body (handy to check if something exists), and OPTIONS asks which methods a URL allows. Browsers send OPTIONS on their own for cross-origin checks, as you will see in the CORS lesson.

The shortcut

Say the request as a sentence: "[verb] the [noun]." If the sentence sounds wrong, the method is wrong.

Choosing methods for BookNookStep 1 of 4

  1. "Mark book 42 as damaged"

    Only one field changes, so "patch book 42": PATCH /v1/books/42 with {"condition": "damaged"}.

The trap is GET /v1/books/42/delete. A link checker or a browser prefetch following that URL would delete a book, because everyone assumes GET is safe.

Drills

Answer fast — trust the rule.

quick drill

Which method should change only a book's shelf field?

quick drill

Which of these methods is NOT idempotent?

quick drill

A client sends PUT /v1/books/42 with only {"shelf": "B3"}. By the meaning of PUT, what should book 42 become?

quick drill

Why is GET /v1/loans/901/cancel a bad design?

Remember

  • The URL is the noun; the method is the verb.
  • Shortcut: say "[verb] the [noun]" out loud and check it sounds right.
  • Trap: changing data with GET, and using PUT for a partial update.

Practice — level up

0/1 solved

Write your answer, then compare it with a rubric and a model answer.

ExplainPick the verb

For BookNook, choose a method and URL for: adding a book, changing only a book's shelf, and removing a lost book. Explain why a GET link that deletes a book is dangerous.