Golang code comprehension tools

Software engineers spend a greater part of time reading and understanding programs. Indeed, most of the time it takes to develop a program is spent reading it and making logical conclusion about what it does.

Go programmers are no exception. Thanks to gofmt they should not worry about source code formatting. The machines are better suited to analyse source code and accomplish comprehension tasks than us.

In this article we will explore several of Go comprehension tools that are responsible for locating definitions, ascertaining types of expressions, deducing implementation relation, computing method sets, finding callers/callees, jumping through channels, understanding aliasing.


The oralce is a source analysis tool that answers question about your Go source code. It is installed by executing this command:

$ go get golang.org/x/tools/cmd/oracle

A -pos flag is always required. It defines the current cursor position that should be analysed. The expected value is a bytes offset from the beginning of the file.

These are the subcommands that determines the query to perform:

  • callees show possible targets of selected function call
  • callers show possible callers of selected function
  • callstack show path from callgraph root to selected function
  • definition show declaration of selected identifier
  • describe describe selected syntax: definition, methods, etc
  • freevars show free variables of selection
  • implements show relation for selected type or method
  • peers show send/receive corresponding to selected channel op
  • referrers show all refs to entity denoted by selected identifier
  • what show basic information about the selected syntax node

The -format flag set the output format to:

  • plain an editor-friendly format in which every line of output
  • json structured data in JSON syntax.
  • xml structured data in XML syntax.

Overall, the tools provides an friendly interface for adopting it in different development editor: Vim, Emacs, Atom, IntelliJ and etc.

Let see oracle in action:


Pythia is a browser based user interface for oracle. It is based on the following packages:

Pythia is installed with the following command:

$ go get github.com/fzipp/pythia

The pythia command tool now can be found in $GOPATH/bin/pythia. A specific package can be opened with the following command:

$ pythia net/http 

By default the command opens your default browser:

Pythia in Action

This can be disabled with -open flag:

$ pythia -open=false net/http

The default listening port is :8080. It can be changed via -http flag:

$ pythia -http :9876 net/http

The packages can be filtered out on their build tags:

$ pythia -tags=unix net/http


Godepgraph is a program for generating a dependency graph of Go packages. Use go get command to install it:

$ go get github.com/kisielk/godepgraph

Usually the tool is combined with dot command (graphviz CLI):

// this command will generate dependency graph as svg image
// -s ingores the builtin packages
// -horizontal layout the graphics horizontally
$ godepgraph -s -horizontal github.com/codegangsta/gin | dot -Tsvg -o gin-godepgraph.svg

The command above will produce the following graphics:

Godepgraph in Action

The godepgraph tools can be controlled with these flags:

  • -d show dependencies of packages in the Go standard library
  • -horizontal lay out the dependency graph horizontally instead of vertically
  • -i string a comma-separated list of packages to ignore
  • -p string a comma-separated list of prefixes to ignore
  • -s ignore packages in the Go standard library
  • -t include test packages
  • -tags string a comma-separated list of build tags to consider satisfied during the build


Even though Golang does not have dedicated development environment, software engineers can be very product by adopting some of the comprehensive tools mentioned in this article.

Published by in programming languages, tools and tutorial and tagged #go using 577 words.