A common use for json_last_error_msg is processing data without rebuilding the operation manually. Returns a readable message for the previous JSON encoding or decoding error.
What Is json_last_error_msg in PHP?
Returns a readable message for the previous JSON encoding or decoding error.
Syntax:
json_last_error_msg() : string
Parameters and Return Value
This operation takes no arguments.
Declared return type: string. Distinguish false, an empty result, and exceptions where the API permits them.
Example 1: Basic Usage
This example demonstrates the main operation with a small, controlled input.
<?php
json_decode("{invalid}");
echo json_last_error_msg();
The example focuses on the value produced or the state changed by this API. Review the return value and validate input before using this pattern in production.
Example 2: Another Input
This example changes the input or surrounding setup to illustrate another behavior.
<?php
json_decode("[]");
echo json_last_error_msg();
The example focuses on the value produced or the state changed by this API. Review the return value and validate input before using this pattern in production.
Practical Example
This application-style example shows a self-contained usage pattern and checks its result.
<?php
json_decode("{\"test\":}");
if (json_last_error() !== JSON_ERROR_NONE) { echo json_last_error_msg(); }
The example focuses on the value produced or the state changed by this API. Review the return value and validate input before using this pattern in production.
Important Behavior and Edge Cases
- The last-error message describes the most recent eligible JSON operation, not arbitrary application failures.
- Use the intended input type and handle empty or malformed values explicitly.
- Where this API requires an extension, version, or file, document that dependency before using it in a real application.
Comparison With Related Functions
| Function or Method | When to Use It |
|---|---|
json_last_error_msg | Returns a readable message for the previous JSON encoding or decoding error. |
json_last_error | Returns the error code for the last JSON operation that did not use JSON_THROW_ON_ERROR. |
Common Beginner Mistakes
| Mistake | Correct Approach |
|---|---|
| Using this API without checking the required input or extension | The last-error message describes the most recent eligible JSON operation, not arbitrary application failures. |
| Treating valid JSON as valid business data | Check required keys, types and allowed values after decoding. |
| Ignoring UTF-8 or encoding failures | Use JSON_THROW_ON_ERROR and handle JsonException explicitly. |
Key Takeaways
- Returns a readable message for the previous JSON encoding or decoding error.
- The last-error message describes the most recent eligible JSON operation, not arbitrary application failures.
- Test both the expected case and at least one failure or empty-input case before deployment.
Returns a readable message for the previous JSON encoding or decoding error. Use it when the operation fits your input, output and validation requirements.