Error response format in Rest API - Step-by-Step Execution

Concept Flow - Error response format

Client sends request

↓

Server processes request

↓

Error occurs?

No→Send success response

Yes↓

Create error response

↓

Send error response to client

The client sends a request, the server processes it, and if an error happens, the server creates and sends an error response back.

Execution Sample

Rest API

{
  "error": {
    "code": 404,
    "message": "Resource not found"
  }
}

This JSON shows a typical error response with a code and message.

Execution Table

Step	Action	Condition	Result	Response Sent
1	Client sends request	N/A	Request received by server	No response yet
2	Server processes request	N/A	Checks if resource exists	No response yet
3	Check resource existence	Resource found?	No	No
4	Create error response	Error type: Not Found	Prepare JSON with code 404 and message	No
5	Send error response	N/A	Error JSON sent to client	{"error":{"code":404,"message":"Resource not found"}}
6	Client receives response	N/A	Client sees error message	End

💡 Error response sent because resource was not found

Variable Tracker

Variable	Start	After Step 2	After Step 4	Final
request	empty	received with resource path	same	same
resource_exists	unknown	checked: false	false	false
error_response	none	none	{"code":404,"message":"Resource not found"}	{"code":404,"message":"Resource not found"}

Key Moments - 2 Insights

Why does the server send an error response instead of a success response?

Because the resource was not found (see execution_table step 3), the server creates and sends an error response (step 4 and 5).

What does the error response JSON contain?

It contains an error object with a code (404) and a message explaining the error (see execution_table step 4).

Visual Quiz - 3 Questions

Look at the execution table, what is the response sent at step 5?

A {"success":true}

B {"error":{"code":404,"message":"Resource not found"}}

C Empty response

D {"error":{"code":500,"message":"Server error"}}

💡 Hint

Check the 'Response Sent' column at step 5 in the execution_table.

At which step does the server decide the resource does not exist?

A Step 1

B Step 5

C Step 3

D Step 2

💡 Hint

Look at the 'Condition' column in the execution_table to find when resource existence is checked.

If the resource was found, what would change in the execution table?

A Step 3 condition would be Yes and success response sent at step 5

B Error response would still be sent

C No response would be sent

D Server would crash

💡 Hint

Refer to the 'Condition' and 'Response Sent' columns in the execution_table for step 3 and 5.

Concept Snapshot

Error response format:
- Server sends JSON with error details
- Common fields: code (number), message (string)
- Sent when request cannot be fulfilled
- Helps client understand what went wrong
- Example: {"error":{"code":404,"message":"Resource not found"}}

Full Transcript

When a client sends a request to a server, the server processes it. If the requested resource is not found, the server creates an error response in JSON format. This response includes an error code like 404 and a message explaining the problem. The server then sends this error response back to the client. This helps the client know why the request failed. The error response format is a standard way to communicate problems in APIs.