Detect the pitch of any monophonic sound via your microphone and an autocorrelation algorithm. Standard EADGBE + chromatic mode, ±50 cent deviation meter.
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Click Start listening and allow microphone access (your browser will prompt). Pluck a string clearly and sustain it. The detected pitch, closest note name and cent deviation are shown — when the needle sits on 0, you are in tune. In Standard Guitar mode the six reference strings (E2 A2 D3 G3 B3 E4) appear below; the closest one highlights as you play. In Chromatic mode any of the 12 equal-temperament notes is detected. Pitch is found with an autocorrelation algorithm (more accurate for harmonic-rich monophonic sources like guitar strings than a bare FFT). Everything runs locally; no audio leaves your device. HTTPS is required for microphone access — already the case on this site.