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WebREPL client for MicroPython

This repository contains the WebREPL client and related tools, for accessing a MicroPython REPL (interactive prompt) over WebSockets.

To start WebREPL terminal client, clone or download this repository (in full) and open webrepl.html in a browser. Recent versions of Firefox and Chrome (or Chromium) are supported.

The latest version of the client is also hosted online at (note: while it's hosted online, all interaction with your boards still happen locally in your own network).

At this time, WebREPL client cannot be accessed over HTTPS connections. This is due to not widely published policy that HTTPS pages may access only WSS (WebSocket Secure) protocol. This is somewhat similar to warnings issued when e.g. an HTTPS page loads an image over plain HTTP. However, in case of WebSockets, some browsers don't even issue a user-visible warning, and others may word it confusingly, so it's hard to understand that it applies to WebSocket connections. As WebREPL is intended to be used only within a user's local network, HTTPS isn't strictly required, and not accessing webrepl.html over HTTPS is a suggested workaround.

WebREPL file transfer

WebREPL protocol includes experimental support for file transfer. This feature is currently in alpha and has known issues on systems which have it enabled (ESP8266).

To use WebREPL file transfer capabilities, a separate command line utility is provided, (file transfer is not supported via webrepl.html client). Run --help

to see usage information. Note that there can be only one active WebREPL connection, so while webrepl.html is connected to device, can't transfer files, and vice versa.

WebREPL shell provides remote shell using MicroPython WebREPL protocol, and runs with Python 2 as well as Python 3. With wireless connection to MicroPython it is OTA shell (Over-the-air), the main difference to screen WebREPL terminal session.

Run just command for usage information:

$ ./ - remote shell using MicroPython WebREPL protocol
  [-p password] [-dbg] [-r] <host> - remote shell (to <host>:8266)
Examples: -p abcd -p abcd -r < <(sleep 1 && echo "...")
Special command control sequences:
  line with single characters
    'A' .. 'E' - use when CTRL-A .. CTRL-E needed
  just "exit" - end shell
  • "-p" option allows to pass password instead of entering via keyboard, allowing for automation.
  • "-r" option tells that input will be provided by redirection, and that command lines need to be printed (not needed when input is done via keyboard). See last sample execution on how to paste in python code from file and use (without need to upload a module before).
  • "-dbg" option enables additional debug output in case has a problem and is not needed normally.

Previous section on only one active WebREPL connection applies here as well. So you can run shell, then exit, then upload a modified module with to MicroPython, login again into shell and finally reload the module in shell.

Input is invisible on password entry for WebREPL session, as well as in raw mode (raw mode is not available in webrepl.html). Commands can be edited on input, and command history is available.

CTRL-A, CTRL-B, CTRL-C, CTRL-D and CTRL-E on empty line switch between modes. For these have to be entered by A+ENTER, B+ENTER, C+ENTER, D+ENTER, E+ENTER.

Normal mode is correct, as well as paste mode. Raw mode has invisible input, and output ">" is followed by "OK>" for every press of CTRL-D. Only difference to screen session is, that each completed line produces a new line.

Although not documented in raw mode python help, CTRL-D is needed (as in paste mode) before CTRL-B to switch to normal mode, to commit the input lines sofar. CTRL-D can be pressed multiple times before CTRL-B. Beware that you need to have at least one line of input present, otherwise CTRL-D will do a soft reset on target platform.

Soft reset on target platform (by machine.reset() or by CTRL-D on empty input line) hangs session as well as webrepl.html browser session.

Because Micropython issue initial WebREPL prompt on (re)connect is always ">>> ", regardless of real mode (raw/normal/paste). Since needs to wait for prompt being received from target in order to do correct and editable input via "do_input(prompt)", issue 4196 is problematic. Currently this issue is resolved by automatically injecting "CTRL-C CTRL-B" after password has been entered, ending always in normal mode. Because of the "CTRL-B" you see the MicoPython version string message on (re)connect. The injection also helps on terminating endless loops, which was possible before fix of issue 1. Now on endless loop, press "CTRL-C" to terminate and reconnect again. The initial injected "CTRL-C" will stop the endless loop and provide REPL prompt.

Sample session with mode changes and invisible password and raw mode input:

$ ./

WebREPL connected
MicroPython v1.9.4-481-g3cd2c281d on 2018-09-04; ESP module with ESP8266
Type "help()" for more information.
>>> A
raw REPL; CTRL-B to exit

MicroPython v1.9.4-481-g3cd2c281d on 2018-09-04; ESP module with ESP8266
Type "help()" for more information.
>>> a
>>> E
paste mode; Ctrl-C to cancel, Ctrl-D to finish
=== a=43
=== C
>>> a
>>> E
paste mode; Ctrl-C to cancel, Ctrl-D to finish
=== a=43
=== D

>>> a
>>> 4**3**2
>>> exit
### closed ###

Sample session with password on command line and redirect:

$ ./ -p abcd -r < <(sleep 1 && echo "E" && cat && echo -e "D\nc(7)\nexit")
WebREPL connected
MicroPython v1.9.4-481-g3cd2c281d on 2018-09-04; ESP module with ESP8266
Type "help()" for more information.
>>> E
paste mode; Ctrl-C to cancel, Ctrl-D to finish
=== def s(x):
===     return x*x
=== def c(x):
===     return x*s(x)
=== D

>>> c(7)
>>> exit
### closed ###

Both, as well as, do not run on MicroPython. Using danni's uwebsockets repo a simple (OTA) shell can be run from one MicroPython module on a second MicroPython module:

Technical details

WebREPL is the latest standard (in the sense of an Internet RFC) for communicating with and controlling a MicroPython-based board. Following were the requirements for the protocol design:

  1. Single connection/channel, multiplexing terminal access, filesystem access, and board control.

  2. Network ready and Web technologies ready (allowing access directly from a browser with an HTML-based client).

Based on these requirements, WebREPL uses a single connection over WebSocket as a transport protocol. Note that while WebREPL is primarily intended for network (usually, wireless) connection, due to its single-connection, multiplexed nature, the same protocol can be used over a lower-level, wired connection like UART, SPI, I2C, etc.

Few other traits of WebREPL:

  1. It is intended (whenever possible) to work in background, i.e. while WebREPL operations are executed (like a file transfer), normal REPL/user application should continue to run and be responsive (though perhaps with higher latency, as WebREPL operations may take its share of CPU time and other system resources). (Some systems may not allow such background operation, and then WebREPL access/operations will be blocking).

  2. While it's intended to run in background, like a Unix daemon, it's not intended to support multiple, per-connection sessions. There's a single REPL session, and this same session is accessible via different media, like UART or WebREPL. This also means that there's usually no point in having more than one WebREPL connection (multiple connections would access the same session), and a particular system may actually limit number of concurrent connections to ease implementation and save system resources.

WebREPL protocol consists of 2 sub-protocols:

  • Terminal protocol

This protocol is finalized and is very simple in its nature, akin to Telnet protocol. WebSocket "text"-flagged messages are used to communicate terminal input and output between a client and a WebREPL- enabled device (server). There's a guaranteed password prompt, which can be detected by the appearance of characters ':', ' ' (at this point, server expected a password ending with '\n' from client). If you're interested in developing a 3rd-party application to communicate using WebREPL terminal protocol, the information above should be enough to implement it (or feel free to study implementation of the official clients in this repository).

  • File transfer/board control protocol

This protocol uses WebSocket "binary"-flagged messages. At this point, this protocol is in early research/design/proof-of-concept phase. The only available specification of it is the reference code implementation, and the protocol is subject to frequent and incompatible changes. The module mentioned above intended to be both a command-line tool and a library for 3rd-party projects to use, though it may not be there yet. If you're interested in integrating WebREPL transfer/control capabilities into your application, please submit a ticket to GitHub with information about your project and how it is useful to MicroPython community, to help us prioritize this work.

While the protocol is (eventually) intended to provide full-fledged filesystem access and means to control a board (all subject to resource constraints of a deeply embedded boards it's intended to run on), currently, only "get file" and "put file" operations are supported. As above, sharing information with us on features you miss and how they can be helpful to the general MicroPython community will help us prioritize our plans. If you're interested in reducing wait time for new features, you're also welcome to contribute to their implementation. Please start with discussing the design first, and with small changes and improvements. Please keep in mind that WebREPL is just one of the many features on which MicroPython developers work, so having sustainable (vs revolutionary) development process is a must to have long-term success.


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