How to validation API inputs?

Harry 608 27 Jan 2026

Harry 27 Jan 2026

API input validation means checking incoming data to make sure it’s correct, safe, and expected before processing it.

Check required fields
Ensure mandatory parameters are present.
Example: email, password must not be empty.
Validate data types
Confirm inputs match expected types (string, number, boolean, array).
Apply format rules
Use patterns or rules:
- Email format
- Date format (ISO 8601)
- Phone number pattern
Set length & range limits
- String length (min/max)
- Number range (e.g., age 1–120)
Whitelist allowed values
Accept only known values (e.g., role = admin | user).
Sanitize inputs
Remove or escape harmful characters to prevent SQL injection, XSS, etc.
Use validation libraries
Examples:
- Node.js: Joi, Yup, Zod
- Java: Hibernate Validator
- Python: Pydantic, Marshmallow
Return clear error responses
Send meaningful messages with proper HTTP status codes (e.g., 400 Bad Request).

Best practice: Validate inputs at the API boundary before business logic runs.

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