Become a better developer.

A weekly exploration into topics to make you a better Ruby dev.

Our latest issue was about 19 hours ago: Time Off

How to Read Ruby Documentation

Trying to go from being a beginner to an intermediate programmer can seem like running toward a constantly moving finish line. Tutorials are great, but they can only take you through a set use case, and you still might not understand what’s going on under the hood.

One thing I’ve noticed: beginners use tutorials while experienced programmers read and refer to documentation. If you’re going to move past being a beginner, you need to become comfortable with docs.

I thought it would be interesting to devote an article entirely to the Ruby docs. I want to clear up misconceptions about using docs, how to understand them, and how to use them more effectively.

When should you use the documentation?

The documentation is only useful when you have a question about how a specific class, method or module works.

For example, you might want to “remove whitespace around a string.” You might do a google search and find a Stack Overflow post that references String#strip.

Now you’re ready to use the Ruby documentation. Head over to and search for String#strip.

Why the extra step? Why not just use Stack Overflow? Stack Overflow works as an introduction to a concept, but the questions are usually too specific. Plus, the answer could be too complicated or use that specific class, method, or module differently than you intend to. It might work for you now, but not the next time you need to use it.

Use StackOverflow as a jumping-off point to get to Ruby docs rather than the answer unto itself.

Anatomy of a doc

Nobody expects you to read the Ruby documentation like you would read a book. Instead, you should use it like a dictionary.

For example, I may know I need to use the String#index method to find the position of a character in a string. So I’ll go to the docs looking for three pieces of information:

  1. Arguments: What type of arguments does the method expect?
  2. Return Value: What type of object does it return?
  3. Operation: What does the method actually do?

Here’s a link to the documentation for the String#index method. I’ve screenshotted it for your convenience.

String#index documentation

Now lets look at each section in turn.

Method signatures

At the top of the method’s documentation, you’ll see this:

index(substring [, offset]) → fixnum or nil

This is what’s called a “method signature.” It lists the arguments and return values for one form of the method.

Ruby method signatures follow the pattern:

method_name(required_argument [, optional_argument]) → return_types 

So far we can deduce the following about String#index:

  • It has one required argument: a string
  • It has one optional argument: an offset
  • It returns either a number or nil.

If you’ve been paying attention you may have noticed that the documentation for String#index actually has two method signatures. This is very common, and the description that follows applies to both method signatures.

index(regexp [, offset]) → fixnum or nil

Note that the only difference between the two signatures is the first argument. In the first method signature it was a string. In the second one it’s a regular expression i.e. a regexp.

Now, if you were to ask me about String#index I could tell you: “It requires one argument, either a string or a regular expression. There’s an optional second argument. It returns either a number or nil.”

The Description

Knowing the method signature is great, but so far we’ve only seen half of the picture. We know its inputs and outputs but we don’t know what it does.

And if we’re being honest, we don’t really know what some of the inputs are. For example, I’m not 100% sure what the offset argument does.

These details are usually cleared up in the description:

Returns the index of the first occurrence of the given substring or pattern (regexp) in str. Returns nil if not found. If the second parameter is present, it specifies the position in the string to begin the search.

It’s all clear now! I would attempt to summarize this for you but the summary would be longer than the original text. After all, this a relatively short description. String#index is a pretty straightforward method.

Many method descriptions are more complex. They can seem overwhelming. However if you look closely you will find that most of them follow an if-then structure:

  • “If passed a single index, returns a substring of one character at that index.”
  • “If pattern is a String, then its contents are used as the delimiter when splitting str.”
  • “If the increment generates a “carry,” the character to the left of it is incremented.”

Once you understand this pattern, it’s much easier to skim over the statements and see if any of them apply to your particular use case.


Many of Ruby’s methods come with usage examples. While they’re often quite helpful it’s good to keep in mind that they’re only intended to illustrate how to use the method. They’re not necessarily suitable to be copy-pasted directly into your production code.

Use the examples and the descriptions as a way to understand the concept while using the signature as a guide to use and syntax.

Bottom line

I hope this post helped make sense of how to approach RubyDocs to help you move from tutorials to documentation. Once you know how to approach RubyDocs, your understanding of applying your Ruby knowledge will grow.

Get our weekly email about topics that will make you a better engineer. (Newest: Metaprogramming)