Plumber allows you to create a web API by merely decorating your existing R source code with roxygen2-like comments. Take a look at an example.

# plumber.R

#* Echo back the input
#* @param msg The message to echo
#* @get /echo
function(msg="") {
  list(msg = paste0("The message is: '", msg, "'"))
}

#* Plot a histogram
#* @serializer png
#* @get /plot
function() {
  rand <- rnorm(100)
  hist(rand)
}

#* Return the sum of two numbers
#* @param a The first number to add
#* @param b The second number to add
#* @post /sum
function(a, b) {
  as.numeric(a) + as.numeric(b)
}

These comments allow plumber to make your R functions available as API endpoints. You can use either #* as the prefix or #', but we recommend the former since #' will collide with roxygen2.

library(plumber)
# 'plumber.R' is the location of the file shown above
pr("plumber.R") %>%
  pr_run(port=8000)

You can visit this URL using a browser or a terminal to run your R function and get the results. For instance http://localhost:8000/plot will show you a histogram, and http://localhost:8000/echo?msg=hello will echo back the 'hello' message you provided.

Here we're using curl via a Mac/Linux terminal.

$ curl "http://localhost:8000/echo"
 {"msg":["The message is: ''"]}
$ curl "http://localhost:8000/echo?msg=hello"
 {"msg":["The message is: 'hello'"]}

As you might have guessed, the request's query string parameters are forwarded to the R function as arguments (as character strings).

$ curl --data "a=4&b=3" "http://localhost:8000/sum"
 [7]

You can also send your data as JSON:

$ curl -H "Content-Type: application/json" --data '{"a":4, "b":5}' http://localhost:8000/sum
 [9]

You can install the latest stable version from CRAN using the following command:

install.packages("plumber")

If you want to try out the latest development version, you can install it from GitHub.

remotes::install_github("rstudio/plumber")
library(plumber)

If you're just getting started with hosting cloud servers, the DigitalOcean integration included in plumber will be the best way to get started. You'll be able to get a server hosting your custom API in just two R commands. To deploy to DigitalOcean, check out the plumber companion package plumberDeploy.

RStudio Connect is a commercial publishing platform that enables R developers to easily publish a variety of R content types, including Plumber APIs. Additional documentation is available at https://www.rplumber.io/articles/hosting.html#rstudio-connect-1.

A couple of other approaches to hosting plumber are also made available:

• PM2 - https://www.rplumber.io/articles/hosting.html#pm2-1
• Docker - https://www.rplumber.io/articles/hosting.html#docker

• OpenCPU - A server designed for hosting R APIs with an eye towards scientific research.
• jug - (development discontinued) an R package similar to Plumber but uses a more programmatic approach to constructing the API.