Data validation

Ensures that incoming data conforms to expected formats and constraints before further processing.

Web API: validating JSON payload fields before business logic execution Command-line tool: checking argument types and value ranges at startup File parser: verifying header signatures and field lengths before reading the file body

Web services, command-line applications, data pipelines, microservices, desktop utilities

validate input → reject or sanitize → proceed with processing

• schema
• constraints
• validator
• sanitize
• raise error
• type check

• Manual if‑else checks vs. dedicated validation libraries – manual checks are lightweight but repeatable
• libraries provide reusable schemas and clearer error reporting

Using loose equality (==) for type checks – allows unintended type coercion and lets invalid data pass Validating only a subset of fields – leads to hidden bugs when unchecked fields are later used Raising generic exceptions on validation failure – makes error handling ambiguous for callers

Sanitization: cleans data after it has been accepted, whereas validation rejects non‑conforming data upfront Type checking: static analysis performed at compile time, while input validation occurs at runtime Error handling: deals with failures after they occur; validation aims to prevent failures

Coming from JavaScript: using == for comparisons in validation → may coerce types and accept invalid values; use === or explicit type checks instead.

• Sanitization
• Type checking
• Error handling

Do not use heavy validation for performance‑critical inner loops; prefer lightweight checks or assume trusted data Complex schema validation can introduce noticeable latency; cache compiled validators when possible Boundary conditions such as empty strings or zero values must be explicitly allowed or rejected depending on business rules

Proper input validation prevents security vulnerabilities, data corruption, and runtime crashes, leading to more robust and maintainable production systems.

Think of a security guard at a building entrance: only people with the right badge (valid data) are let through, everyone else is turned away.