Which ESP8266 / ESP32 pins are safe to use?

Not every pin on a NodeMCU or ESP32 DevKit is a good choice. Some are strapping pins that decide the boot mode (pull them the wrong way and the board won't start), some are wired to the onboard flash chip, some are input-only, and on the ESP32 the ADC2 channels stop working while WiFi is active. This reference marks every pin as safe, use-with-care or avoid, and shows its peripherals (ADC, PWM, I2C, SPI, UART, touch, DAC).

Click any pin for details, or use the filter chips to highlight all pins of a peripheral — handy when planning sensor wiring for MQTT / Home Assistant projects.