As with [flashing](flash.md) there are several ways to upload code from your computer to the device.

!!! note

	The NodeMCU serial interface uses 115'200bps at boot time. To change the speed after booting, issue `uart.setup(0,9600,8,0,1,1)`. If the device panics and resets at any time, errors will be written to the serial interface at 115'200 bps.

## Tools
Transferring application code to ESP8266/8285 is an essential task, one that you'll perform quite frequently. Hence, it does make sense to try a few different uploading tools until you find one you feel comfortable with. [https://frightanic.com/iot/tools-ides-nodemcu/](https://frightanic.com/iot/tools-ides-nodemcu/) lists almost a dozen classical uploaders - in addition to IDEs or IDE-like applications which of course transfer code as well.

The NodeMCU firmware team does not give any recommendations as for which uploader to use nor are there any "NodeMCU approved" tools. The below listed tools are just three, in no particular order, which seem popular and/or reasonably well maintained.

### ESPlorer

> The essential multiplatforms tools for any ESP8266 developer from luatool author’s, including Lua for NodeMCU and MicroPython. Also, all AT commands are supported. Requires Java (Standard Edition - SE ver 7 and above) installed.

![ESPlorer](img/ESPlorer.jpg "ESPlorer")

Source: [https://github.com/4refr0nt/ESPlorer](https://github.com/4refr0nt/ESPlorer)

Supported platforms: macOS, Linux, Windows, anything that runs Java

### nodemcu-uploader.py

> A simple tool for uploading files to the filesystem of an ESP8266 running NodeMCU as well as some other useful commands.

Source: [https://github.com/kmpm/nodemcu-uploader](https://github.com/kmpm/nodemcu-uploader)

Supported platforms: macOS, Linux, Windows, anything that runs Python

### NodeMCU-Tool

> Upload/Download Lua files to your ESP8266 module with NodeMCU firmware.
> Simple. Command Line. Cross-Platform. File Management. NodeMCU.

Source: [https://github.com/andidittrich/NodeMCU-Tool](https://github.com/andidittrich/NodeMCU-Tool)

Supported platforms: macOS, Linux Windows, anything that runs Node.js

## init.lua
You will see "lua: cannot open init.lua" printed to the serial console when the device boots after it's been freshly flashed. If NodeMCU finds a `init.lua` in the root of the file system it will execute it as part of the boot sequence (standard Lua feature). Hence, your application is initialized and triggered from `init.lua`. Usually you first set up the WiFi connection and only continue once that has been successful.

Be very careful not to lock yourself out! If there's a bug in your `init.lua` you may be stuck in an infinite reboot loop. It is, therefore, advisable to build a small delay into your startup sequence that would allow you to interrupt the sequence by e.g. deleting or renaming `init.lua` (see also [FAQ](lua-developer-faq.md#how-do-i-avoid-a-panic-loop-in-initlua)). Your `init.lua` is most likely going to be different than the one below but it's a good starting point for customizations:

```lua
-- load credentials, 'SSID' and 'PASSWORD' declared and initialize in there
dofile("credentials.lua")

function startup()
    if file.open("init.lua") == nil then
        print("init.lua deleted or renamed")
    else
        print("Running")
        file.close("init.lua")
        -- the actual application is stored in 'application.lua'
        -- dofile("application.lua")
    end
end

-- Define WiFi station event callbacks
wifi_connect_event = function(T)
  print("Connection to AP("..T.SSID..") established!")
  print("Waiting for IP address...")
  if disconnect_ct ~= nil then disconnect_ct = nil end
end

wifi_got_ip_event = function(T)
  -- Note: Having an IP address does not mean there is internet access!
  -- Internet connectivity can be determined with net.dns.resolve().
  print("Wifi connection is ready! IP address is: "..T.IP)
  print("Startup will resume momentarily, you have 3 seconds to abort.")
  print("Waiting...")
  tmr.create():alarm(3000, tmr.ALARM_SINGLE, startup)
end

wifi_disconnect_event = function(T)
  if T.reason == wifi.eventmon.reason.ASSOC_LEAVE then
    --the station has disassociated from a previously connected AP
    return
  end
  -- total_tries: how many times the station will attempt to connect to the AP. Should consider AP reboot duration.
  local total_tries = 75
  print("\nWiFi connection to AP("..T.SSID..") has failed!")

  --There are many possible disconnect reasons, the following iterates through
  --the list and returns the string corresponding to the disconnect reason.
  for key,val in pairs(wifi.eventmon.reason) do
    if val == T.reason then
      print("Disconnect reason: "..val.."("..key..")")
      break
    end
  end

  if disconnect_ct == nil then
    disconnect_ct = 1
  else
    disconnect_ct = disconnect_ct + 1
  end
  if disconnect_ct < total_tries then
    print("Retrying connection...(attempt "..(disconnect_ct+1).." of "..total_tries..")")
  else
    wifi.sta.disconnect()
    print("Aborting connection to AP!")
    disconnect_ct = nil
  end
end

-- Register WiFi Station event callbacks
wifi.eventmon.register(wifi.eventmon.STA_CONNECTED, wifi_connect_event)
wifi.eventmon.register(wifi.eventmon.STA_GOT_IP, wifi_got_ip_event)
wifi.eventmon.register(wifi.eventmon.STA_DISCONNECTED, wifi_disconnect_event)

print("Connecting to WiFi access point...")
wifi.setmode(wifi.STATION)
wifi.sta.config({ssid=SSID, pwd=PASSWORD})
-- wifi.sta.connect() not necessary because config() uses auto-connect=true by default

```

## Compiling Lua on your PC for Uploading

If you install Lua on your development PC or Laptop, then you can use a standard `lua` environment to develop PC applications and also use the standard `luac` compiler to syntax check _any_ Lua source code. However because of architectural differences between the ESP8266 chipset with its SDK and a standard PC CPU, the system APIs are different and the binary output from the standard PC `luac` cannot be run on the ESP8266.

To address this issue,  the standard NodeMCU make now generates a host executable `lua.cross` (or `lua.cross.int` for integer builds) as well as the firmware binary itself.  Compiling source on one platform for use on another is known as _cross-compilation_ and this `luac.cross` compiler allows you to compile Lua source files on your PC for downloading onto ESP8266 in a binary format.

The firmware also includes API calls to allow Lua sources to be compiled on ESP, but this mode of compilation is limited by the RAM heap available. Host cross compilation bypasses this ESP compile limit entirely and allows you to use larger modules within your code.  In the case of LFS compiles,  this code is stored in flash memory on the ESP, and so has no RAM overhead; the only limit is the size of the allocated LFS region.

