Human-readable error messages in Rest API

Introduction

Human-readable error messages help users understand what went wrong in simple words. They make fixing problems easier and improve user experience.

When an API request fails and you want to tell the user why.

When validating user input and some data is missing or incorrect.

When a server error happens and you want to explain it clearly.

When a user tries to access something they don't have permission for.

When a resource is not found and you want to inform the user politely.

Syntax

Rest API

{
  "error": {
    "code": "string",
    "message": "string",
    "details": "string (optional)"
  }
}

The code is a short identifier for the error.

The message is a clear, simple explanation for the user.

Examples

This message tells the user their email input is wrong.

Rest API

{
  "error": {
    "code": "INVALID_INPUT",
    "message": "Your email address is not valid."
  }
}

This message explains a missing item with extra details.

Rest API

{
  "error": {
    "code": "NOT_FOUND",
    "message": "The requested item was not found.",
    "details": "Item ID 123 does not exist."
  }
}

Sample Program

This simple API returns a user name by ID. If the user ID is missing, it sends a human-readable error message with a 404 status.

Rest API

from flask import Flask, jsonify, request

app = Flask(__name__)

@app.route('/user/<int:user_id>')
def get_user(user_id):
    users = {1: 'Alice', 2: 'Bob'}
    if user_id not in users:
        return jsonify({
            "error": {
                "code": "NOT_FOUND",
                "message": f"User with ID {user_id} was not found."
            }
        }), 404
    return jsonify({"user": users[user_id]})

if __name__ == '__main__':
    app.run(debug=True)

Important Notes

Keep messages short and clear, avoiding technical terms.

Use consistent error codes to help developers handle errors easily.

Include extra details only if they help the user fix the problem.

Summary

Human-readable error messages explain problems in simple words.

They improve user experience and help fix issues faster.

Use clear codes and messages in your API responses.

Practice

1.

What is the main purpose of human-readable error messages in a REST API?

easy

A. To confuse users with complex codes

B. To hide all error details from users

C. To make error messages as technical as possible

D. To explain problems in simple words for users

Solution

1. Step 1: Understand the role of error messages

   Error messages should help users understand what went wrong.

2. Step 2: Identify the best description

   Human-readable means simple and clear, not technical or confusing.

3. Final Answer:

   To explain problems in simple words for users -> Option D

4. Quick Check:

   Human-readable = simple explanation [OK]

Hint: Think: error messages should help, not confuse [OK]

Common Mistakes:

• Choosing technical jargon instead of simple words
• Assuming error messages should hide details
• Confusing human-readable with code-only messages

2.

Which of the following is the correct JSON format for a human-readable error message in a REST API response?

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

easy

A. { error: 404, message: 'Not found' }

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

C. { "code": 404, "msg": "Not found" }

D. { error_code: 404, error_message: 'Resource missing' }

Solution

1. Step 1: Check JSON syntax correctness

   Valid JSON requires double quotes around keys and string values.

2. Step 2: Match the expected structure

   The error object should contain code and message keys with clear names.

3. Final Answer:

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

4. Quick Check:

   Valid JSON with clear keys = { "error": { "code": 404, "message": "Resource not found" } } [OK]

Hint: Look for double quotes and clear key names in JSON [OK]

Common Mistakes:

• Using single quotes instead of double quotes in JSON
• Missing nested error object structure
• Using incorrect key names like 'msg' or 'error_code'

3.

Given this API response code snippet, what will be the output message?

response = {
  "status": 400,
  "error": {
    "code": "INVALID_INPUT",
    "message": "Input value is not valid"
  }
}
print(response["error"]["message"])

medium

A. Input value is not valid

B. 400

C. INVALID_INPUT

D. KeyError

Solution

1. Step 1: Access nested dictionary keys

   response["error"] gives the nested dictionary, then ["message"] accesses the message string.

2. Step 2: Print the message value

   The value of response["error"]["message"] is "Input value is not valid".

3. Final Answer:

   Input value is not valid -> Option A

4. Quick Check:

   Nested key access = message string [OK]

Hint: Follow dictionary keys step-by-step to find the message [OK]

Common Mistakes:

• Printing the error code instead of message
• Confusing status code with error message
• Trying to access keys incorrectly causing KeyError

4.

Identify the error in this REST API error response JSON and fix it for proper human-readable message format:

{
  error: {
    code: 401,
    message: 'Unauthorized access'
  }
}

medium

A. Remove the error object and keep only code and message

B. Change code 401 to string '401'

C. Replace single quotes with double quotes and add quotes around keys

D. Add a status key with value 'error'

Solution

1. Step 1: Check JSON syntax rules

   JSON keys and string values must be in double quotes, not single quotes or unquoted.

2. Step 2: Fix the JSON format

   Add double quotes around keys (error, code, message) and change single quotes to double quotes.

3. Final Answer:

   Replace single quotes with double quotes and add quotes around keys -> Option C

4. Quick Check:

   Valid JSON needs double quotes on keys and strings [OK]

Hint: JSON keys and strings always need double quotes [OK]

Common Mistakes:

• Using single quotes for strings in JSON
• Leaving keys unquoted causing syntax errors
• Changing numeric codes to strings unnecessarily

5.

You want to design a REST API error response that helps users fix input errors quickly. Which approach is best?

{
  "error": {
    "code": "INVALID_EMAIL",
    "message": "Email format is incorrect",
    "field": "email",
    "suggestion": "Use a valid email like [e-mail]"
  }
}

hard

A. Include error code, message, field name, and suggestion for fix

B. Only include a generic error message without details

C. Return HTTP 200 status with error details inside

D. Send error details only in server logs, not in response

Solution

1. Step 1: Identify helpful error response elements

   Clear code, message, field, and suggestion guide users to fix errors.

2. Step 2: Compare options for user-friendliness

   Include error code, message, field name, and suggestion for fix provides detailed, human-readable info; others hide or confuse users.

3. Final Answer:

   Include error code, message, field name, and suggestion for fix -> Option A

4. Quick Check:

   Detailed, clear errors improve user experience [OK]

Hint: Add suggestions and field info for clearer error messages [OK]

Common Mistakes:

• Returning generic messages without guidance
• Using HTTP 200 for errors causing confusion
• Hiding error details from users