Verifier
A program that scores whether an output is correct — the reward source in reinforcement learning from verifiable rewards.
A verifier is an automatic check that decides pass or fail for a model’s output: a unit test, a math-answer comparison, a schema validator. In RLVR it replaces a learned reward model, so training signal comes from ground truth rather than a gameable proxy. A sound verifier is critical — every false positive is a lie the model learns to exploit.