This documentation is for version 2.2.0. Other versions.

Table of Contents

WiFi(ESP8266WiFi library)

This is mostly similar to WiFi shield library. Differences include:

WiFiServer, WiFiClient, and WiFiUDP behave mostly the same way as with WiFi shield library. Four samples are provided for this library. You can see more commands here:


Library for calling functions repeatedly with a certain period. Two examples included.

It is currently not recommended to do blocking IO operations (network, serial, file) from Ticker callback functions. Instead, set a flag inside the ticker callback and check for that flag inside the loop function.

Here is library to simplificate Ticker usage and avoid WDT reset: TickerScheduler


This is a bit different from standard EEPROM class. You need to call EEPROM.begin(size) before you start reading or writing, size being the number of bytes you want to use. Size can be anywhere between 4 and 4096 bytes.

EEPROM.write does not write to flash immediately, instead you must call EEPROM.commit() whenever you wish to save changes to flash. EEPROM.end() will also commit, and will release the RAM copy of EEPROM contents.

EEPROM library uses one sector of flash located just after the SPIFFS.

Three examples included.

I2C (Wire library)

Wire library currently supports master mode up to approximately 450KHz. Before using I2C, pins for SDA and SCL need to be set by calling Wire.begin(int sda, int scl), i.e. Wire.begin(0, 2) on ESP-01, else they default to pins 4(SDA) and 5(SCL).


SPI library supports the entire Arduino SPI API including transactions, including setting phase (CPHA). Setting the Clock polarity (CPOL) is not supported, yet (SPI_MODE2 and SPI_MODE3 not working).


An ESP8266 port of SoftwareSerial library done by Peter Lerup (@plerup) supports baud rate up to 115200 and multiples SoftwareSerial instances. See if you want to suggest an improvement or open an issue related to SoftwareSerial.

ESP-specific APIs

APIs related to deep sleep and watchdog timer are available in the ESP object, only available in Alpha version.

ESP.deepSleep(microseconds, mode) will put the chip into deep sleep. mode is one of WAKE_RF_DEFAULT, WAKE_RFCAL, WAKE_NO_RFCAL, WAKE_RF_DISABLED. (GPIO16 needs to be tied to RST to wake from deepSleep.)

ESP.restart() restarts the CPU.

ESP.getResetReason() returns String containing the last reset resaon in human readable format.

ESP.getFreeHeap() returns the free heap size.

ESP.getChipId() returns the ESP8266 chip ID as a 32-bit integer.

Several APIs may be used to get flash chip info:

ESP.getFlashChipId() returns the flash chip ID as a 32-bit integer.

ESP.getFlashChipSize() returns the flash chip size, in bytes, as seen by the SDK (may be less than actual size).

ESP.getFlashChipSpeed(void) returns the flash chip frequency, in Hz.

ESP.getCycleCount() returns the cpu instruction cycle count since start as an unsigned 32-bit. This is useful for accurate timing of very short actions like bit banging.

ESP.getVcc() may be used to measure supply voltage. ESP needs to reconfigure the ADC at startup in order for this feature to be available. Add the following line to the top of your sketch to use getVcc:


TOUT pin has to be disconnected in this mode.

Note that by default ADC is configured to read from TOUT pin using analogRead(A0), and ESP.getVCC() is not available.

mDNS and DNS-SD responder (ESP8266mDNS library)

Allows the sketch to respond to multicast DNS queries for domain names like "foo.local", and DNS-SD (service dicovery) queries. See attached example for details.

SSDP responder (ESP8266SSDP)

SSDP is another service discovery protocol, supported on Windows out of the box. See attached example for reference.

DNS server (DNSServer library)

Implements a simple DNS server that can be used in both STA and AP modes. The DNS server currently supports only one domain (for all other domains it will reply with NXDOMAIN or custom status code). With it clients can open a web server running on ESP8266 using a domain name, not an IP address. See attached example for details.


This library exposes the ability to control RC (hobby) servo motors. It will support upto 24 servos on any available output pin. By defualt the first 12 servos will use Timer0 and currently this will not interfere with any other support. Servo counts above 12 will use Timer1 and features that use it will be effected. While many RC servo motors will accept the 3.3V IO data pin from a ESP8266, most will not be able to run off 3.3v and will require another power source that matches their specifications. Make sure to connect the grounds between the ESP8266 and the servo motor power supply.

Other libraries (not included with the IDE)

Libraries that don't rely on low-level access to AVR registers should work well. Here are a few libraries that were verified to work: