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Aisalkyn Aidarova
Aisalkyn Aidarova

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What is Status Code?

When frontend calls backend, server responds with:

Status Code + Response
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👉 Status code tells:

  • success
  • error
  • what happened

✅ 1xx — Informational (Rare)

Code Meaning
100 Continue
101 Switching Protocols

👉 Usually not used in your API testing

✅ 2xx — SUCCESS (Most Important)

Code Meaning When used
200 OK GET success
201 Created POST success
202 Accepted Request accepted (async)
204 No Content Success but no response body

🔥 Examples

```http id="hwl2wr"
GET /users → 200 OK






```http id="tsmz92"
POST /users → 201 Created
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```http id="21npr6"
DELETE /users/4 → 204 No Content




---

# ✅ 3xx — REDIRECTION

| Code | Meaning                    |
| ---- | -------------------------- |
| 301  | Moved Permanently          |
| 302  | Found (temporary redirect) |
| 304  | Not Modified               |

👉 Mostly browser-related, not common in API testing

---

# ✅ 4xx — CLIENT ERRORS (VERY IMPORTANT)

👉 Problem from **user/request side**

| Code | Meaning              | Example            |
| ---- | -------------------- | ------------------ |
| 400  | Bad Request          | Missing JSON field |
| 401  | Unauthorized         | No login/token     |
| 403  | Forbidden            | No permission      |
| 404  | Not Found            | Wrong URL or ID    |
| 405  | Method Not Allowed   | Wrong HTTP method  |
| 409  | Conflict             | Duplicate data     |
| 422  | Unprocessable Entity | Validation failed  |

---

### 🔥 Examples



```http id="33rrv1"
GET /users/999 → 404 Not Found
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```http id="9flkqn"
POST without body → 400 Bad Request




---

# ✅ 5xx — SERVER ERRORS (VERY IMPORTANT)

👉 Problem from **backend/server**

| Code | Meaning               |
| ---- | --------------------- |
| 500  | Internal Server Error |
| 502  | Bad Gateway           |
| 503  | Service Unavailable   |
| 504  | Gateway Timeout       |

---

### 🔥 Examples



```http id="2lm9mt"
Database crash → 500
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```http id="d4bf3k"
Server overloaded → 503




---

# 🔥 WHAT YOU SHOULD USE IN YOUR API

### Your current backend:

#### GET



```js id="tj9xjs"
res.json(users);
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👉 Returns:

200 OK
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POST

```js id="hcn8wp"
res.status(201).json(newUser);




👉 Correct:



```id="kxj6h8"
201 Created
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PUT

```js id="c3yo0x"
res.json(user);




👉 Should be:



```id="h9n83j"
200 OK
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DELETE

Right now:

```js id="bzgk4x"
res.send("User deleted");




👉 Better (production):



```js id="2p5b6q"
res.status(204).send();
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🔥 INTERVIEW ANSWERS (IMPORTANT)

❓ What status code for POST?

201 Created

❓ What status code if user not found?

404 Not Found

❓ What status code for server error?

500 Internal Server Error

❓ What status code for successful GET?

200 OK

🔥 DEVOPS VIEW

You monitor APIs using status codes:

  • 200 → healthy
  • 4xx → client issue
  • 5xx → system failure (critical alert)

🔥 QUICK CHEAT SHEET 

200 → OK
201 → Created
204 → No Content
400 → Bad Request
401 → Unauthorized
403 → Forbidden
404 → Not Found
500 → Server Error
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