name: api-request-validation description: A skill for implementing robust API request validation in Python web frameworks like FastAPI using Pydantic. Covers Pydantic models, custom validators (email, password), field-level and cross-field validation, query/file validation, and structured error responses. Use when you need to validate incoming API requests.

API Request Validation Skill

Overview

This skill provides guidance and reusable components for implementing robust API request validation in Python, primarily using FastAPI and Pydantic.

It covers:

• Basic validation with Pydantic models.
• Custom validation logic for specific fields.
• Advanced validation scenarios like cross-field validation and query parameters.
• Standardized error handling for validation failures.

Getting Started

The most common validation tasks are broken down into reference files. Start with the one that best fits your needs.

• Basic Validation: If you're new to Pydantic or need to validate a simple data structure, see references/pydantic-models.md.
• Custom Rules: For validating specific formats like emails or password strength, see references/custom-validators.md.
• Complex Scenarios: For validating query parameters, file uploads, or dependencies between fields, see references/advanced-validation.md.
• Error Responses: To customize how validation errors are returned to the client, see references/error-handling.md.

Resources

references/

• pydantic-models.md: Guide to creating basic Pydantic models for request body validation.
• custom-validators.md: How to write custom validator functions for fields.
• advanced-validation.md: Covers cross-field validation, query parameters, and file uploads.
• error-handling.md: Instructions for creating a custom FastAPI exception handler for validation errors.

scripts/

• validators.py: A collection of reusable Pydantic validator functions (e.g., for email, password strength).
• error_handler.py: A pre-built FastAPI exception handler for RequestValidationError.
• main_example.py: A full FastAPI application demonstrating all validation techniques covered in this skill. You can run this file to see the validation in action.