What is the difference between verification and validation?

Verification and validation sound interchangeable, but they answer two different questions. Verification is the inward-facing check: does the implementation match the agreed-upon requirements, designs, and acceptance criteria? Reviews, static analysis, unit tests, and contract tests are mostly verification activities — you have a written truth and you compare the code against it.

Validation is the outward-facing check: even if the code matches the spec, does it actually solve the user's problem in their environment? Usability sessions, beta programs, and exploratory testing against real workflows are validation activities. The classic failure mode is "we built it correctly, but we built the wrong thing."

In practice, most teams need both. A feature can pass every automated check (verification ✅) and still ship a confusing experience that users abandon (validation ❌). Knowing which question you're answering helps you pick the right technique.