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

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?

---

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).

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 a hyphen 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.

The standard best practice for REST APIs is to have a hyphen, not camelcase or underscores.

This comes from Mark Masse's "REST API Design Rulebook" from Oreilly.

In addition, note that Stack Overflow itself uses hyphens in the URL: .../hyphen-underscore-or-camelcase-as-word-delimiter-in-uris

As does WordPress: http://inventwithpython.com/blog/2012/03/18/how-much-math-do-i-need-to-know-to-program-not-that-much-actually

Whilst I recommend hyphens, I shall also postulate an answer that isn't on your list:

Nothing At All

• My company's API has URIs like /quotationrequests/, /purchaseorders/ and so on.
• Despite you saying it was an intranet app, you listed SEO as a benefit. Google does match the pattern /foobar/ in a URL for a query of ?q=foo+bar
• I really hope you do not consider executing a PHP call to any arbitrary string the user passes in to the address bar, as @ServAce85 suggests!

Short Answer:

lower-cased words with a hyphen as separator

Long Answer:

What is the purpose of a URL?

If pointing to an address is the answer, then a shortened URL is also doing a good job. If we don't make it easy to read and maintain, it won't help developers and maintainers alike. They represent an entity on the server, so they must be named logically.

Google recommends using hyphens > Consider using punctuation in your URLs. The URL http://www.example.com/green-dress.html is much more useful to us than http://www.example.com/greendress.html. We recommend that you use hyphens (-) instead of underscores (_) in your URLs.

Coming from a programming background, camelCase is a popular choice for naming joint words.

But RFC 3986 defines URLs as case-sensitive for different parts of the URL. Since URLs are case sensitive, keeping it low-key (lower cased) is always safe and considered a good standard. Now that takes a camel case out of the window.

Source: https://metamug.com/article/rest-api-naming-best-practices.html#word-delimiters

In general, it's not going to have enough of an impact to worry about, particularly since it's an intranet app and not a general-use Internet app. In particular, since it's intranet, SEO isn't a concern, since your intranet shouldn't be accessible to search engines. (and if it is, it isn't an intranet app).

And any framework worth it's salt either already has a default way to do this, or is fairly easy to change how it deals with multi-word URL components, so I wouldn't worry about it too much.

That said, here's how I see the various options:

Hyphen

• The biggest danger for hyphens is that the same character (typically) is also used for subtraction and numerical negation (ie. minus or negative).
• Hyphens feel awkward in URL components. They seem to only make sense at the end of a URL to separate words in the title of an article. Or, for example, the title of a Stack Overflow question that is added to the end of a URL for SEO and user-clarity purposes.

Underscore

• Again, they feel wrong in URL components. They break up the flow (and beauty/simplicity) of a URL, since they essentially add a big, heavy apparent space in the middle of a clean, flowing URL.
• They tend to blend in with underlines. If you expect your users to copy-paste your URLs into MS Word or other similar text-editing programs, or anywhere else that might pick up on a URL and style it with an underline (like links traditionally are), then you might want to avoid underscores as word separators. Particularly when printed, an underlined URL with underscores tends to look like it has spaces in it instead of underscores.

CamelCase

• By far my favorite, since it makes the URLs seem to flow better and doesn't have any of the faults that the previous two options do.
• Can be slightly harder to read for people that have a hard time differentiating upper-case from lower-case, but this shouldn't be much of an issue in a URL, because most "words" should be URL components and separated by a / anyways. If you find that you have a URL component that is more than 2 "words" long, you should probably try to find a better name for that concept.
• It does have a possible issue with case sensitivity, but most platforms can be adjusted to be either case-sensitive or case-insensitive. Any it's only really an issue for 2 cases: a.) humans typing the URL in, and b.) Programmers (since we are not human) typing the URL in. Typos are always a problem, regardless of case sensitivity, so this is no different that all one case.

> It is recommended to use the spinal-case (which is highlighted by > RFC3986), this case is used by Google, PayPal, and other big > companies.

source:- https://blog.restcase.com/5-basic-rest-api-design-guidelines/

EDIT: Although the highlight on the RFC is nowhere to be found, the recommendation on spinal case is still valid (as already noted in other answers)

here's the best of both worlds.

I also "like" underscores, besides all your positive points about them, there is also a certain old-school style to them.

So what I do is use underscores and simply add a small rewrite rule to your Apache's .htaccess file to re-write all underscores to hyphens.

https://yoast.com/apache-rewrite-dash-underscore/