Quality control, or QC, is the process of inspecting work that's already finished, a labeled dataset, a moderation decision, a support ticket, to catch errors before it ships, rather than the broader practices that prevent errors from happening in the first place, which is the territory quality assurance covers instead.

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‍Why it matters

QC and QA often get used interchangeably, but they're not the same. QA is about the guidelines, training, and calibration that reduce errors from happening. QC is about catching whatever slipped through by inspecting the finished output. A team can have solid QA and still run QC, since even well trained, well calibrated people make occasional mistakes.

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‍How it's done

QC usually involves pulling a sample of completed work and checking it against acceptance criteria, functioning as a final gate rather than an ongoing check. If a batch or a decision fails, it typically goes back for correction, and QC results get tracked over time to feed back into QA training and calibration, closing the loop between the two.