Have a Gimlet: A Go JSON/HTTP API Toolkit

Look folks, I made a thing!

It's called gimlet, and it's a Go(lang) tool for making JSON/HTTP APIs (i.e. REST with JSON). Give it a whirl!

It's actually even less a tool, and more of a toolkit or just "a place to put all of the annoying infrastructure that you'll inevitably need when you want to build an JSON/HTTP interface, but that have nothing to do what whatever your API/application does: routing, serializing and serializing JSON.

Nothing hard, nothing terribly interesting, and certainly not anything you couldn't do another way, but, it's almost certainly true that this layer of application infrastructure is totally orthogonal to whatever you application is actually doing, so you should focus on that, and probaly use something like Gimliet.


I'm using the term HTTP/JSON APIs for services where you send and recive JSON data over HTTP. Sometimes people call these REST APIs, and that's not inaccurate, but I think REST is a bit more complicated, and not exactly the core paradigm that I'm pursuing with Gimlet.

Sending and reviving JSON over HTTP makes a lot of sense: there are great tools for parsing JSON and HTTP is a decent high level protocol for interprocess communication between simple data applications. Look up "microservices" at your leisure.

Go is a great language for this it has a lot of tooling that anticipates these kinds of applications, and the deployment model is really friendly to operations teams and systems. Also the static

typing and reasonable separation of private and public interfaces is particularly lovely.

So it should be no surprise that there are a lot tools for building stweb applications, frameworks even. They're great, things like gorilla and negroni are great and provide a very useful set of tools for building Go web apps. Indeed even Gimlet uses components of each of these tools.

The issue, and reason for Gimlet, is that all of these tools assume that you're building a web application, with web pages, static resources, form handling, session state handling, and other things that are totally irrelevant to writing JSON/HTTP interfaces.

So then, Gimlet is a tool to build these kinds of APIs: simple, uses Negroni and Gorilla's mux, and does pretty much everything you need except actually write your code.


Set up the app with some basic configuration:

import "github.com/tychoish/gimlet"

app := gimlet.NewApp()

This sets which port the HTTP server is going to listen for requests and configures the default version of the API. You do want all of your endpoints prefixed with "/v<number>" right? The default version of the API is also avalible without the prefix, or if the version of the route is 0. If you don't set it to 0.

Then register some routes:


app.AddRoute returns an API route object with a set of chainable methods for defining the routes. If you add multiple HTTP methods (GET POST and the like,) then Gimlet automatically defines multiple routes with the same handler for each method.

For handlers, I typically just write functions that take arguments from the top level context (database connections, application configuration, etc) and return``http.HandlerFunc`` objects. For example:

func helloWorld(config *Configuration) http.HandlerFunc {
     return func(w http.ResponseWriter, r *http.Request) {
          input := make(map[string]interface{})
          response := make(map[string]interface{})

          err := gimlet.GetJSON(input)

          // do stuff here

          gimlet.WriteJSON(w, response)

Gimlet has the following functions that parse JSON out of the body of a request, or add JSON output to the body of a response, they are:

  • WriteJSONResponse(w http.ResponseWrite, code int, data interface{})
  • GetJSON(r *http.Request, data interface)

Which read or write data into the interface{} object (typically a struct.) The following three provide consistent response writers for common exit codes:

  • WriteJSON(w http.ResponseWriter, data interface{}) // 200
  • WriteErrorJSON(w http.ResponseWriter, data interface{}) // 400
  • WriteInternalErrorJSON(w http.ResponseWriter, data interface{}) // 500

Finally, when you've written your app, kick it all off, with the following:

err := app.Run()
if err != nil {

And that's it. Enjoy, tell me in the comments or on the issues feed if you find something broken or confusing. Contribution welcome, of course.

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