Hyphen, underscore, or camelCase as word delimiter in URIs?

Question

I'm designing an HTTP-based API for an intranet app. I realize it's a pretty small concern in the grand scheme of things, but: should I use hyphens, underscores, or camelCase to delimit words in the URIs?

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Here are my initial thoughts:

camelCase

• possible issues if server is case-insensitive
• seems to have fairly widespread use in query string keys (http://api.example.com?**searchQuery**=...), but not in other URI parts

Hyphen

• more aesthetically pleasing than the other alternatives
• seems to be widely used in the path portion of the URI
• never seen hyphenated query string key in the wild
• possibly better for SEO (this may be a myth)

Underscore

• potentially easier for programming languages to handle
• several popular APIs (Facebook, Netflix, StackExchange, etc.) are using underscores in all parts of the URI.

I'm leaning towards underscores for everything. The fact that most of the big players are using them is compelling (see https://stackoverflow.com/a/608458/360570).

Answer 1

You should use hyphens in a crawlable web application URL. Why? Because the hyphen separates words (so that a search engine can index the individual words), and is not a word character. Underscore is a word character, meaning it should be considered part of a word.

Double-click this in Chrome: camelCase
Double-click this in Chrome: under_score
Double-click this in Chrome: hyphen-ated

See how Chrome (I hear Google makes a search engine too) only thinks one of those is two words?

camelCase and underscore also require the user to use the shift key, whereas hyphenated does not.

So if you should use hyphens in a crawlable web application, why would you bother doing something different in an intranet application? One less thing to remember.