What is the maximum length of an url?

Question

Does it differ between browsers?

Does the HTTP protocol dictate it?

Answer 1

http://www.boutell.com/newfaq/misc/urllength.html has their own answer based on empirical testing and research. The short answer is that going over 2048 characters makes IE unhappy and thus this is the limit you should use. See page for long answer.

Answer 2

The URI RFC (of which URLs are a subset) doesn't define a maximum length, however, it does recommend that the hostname part of the URI (if applicable) not exceed 255 characters in length:

URI producers should use names that conform to the DNS syntax, even when use of DNS is not immediately apparent, and should limit these names to no more than 255 characters in length.

As noted in other posts though, some browsers have a practical limitation on the length of a URL.

Answer 3

RFC 2616 (Hypertext Transfer Protocol HTTP/1.1) section 3.2.1 says

The HTTP protocol does not place any a priori limit on the length of
a URI. Servers MUST be able to handle the URI of any resource they serve, and SHOULD be able to handle URIs of unbounded length if they provide GET-based forms that could generate such URIs. A server SHOULD return 414 (Request-URI Too Long) status if a URI is longer than the server can handle (see section 10.4.15).

Note: Servers ought to be cautious about depending on URI lengths above 255 bytes, because some older client or proxy implementations might not properly support these lengths.

That's what the standards say. For the reality, see this research over at boutell.com to see what individual browser and server implementations will support. It's worth a read, but the executive summary is:

Extremely long URLs are usually a mistake. URLs over 2,000 characters will not work in the most popular web browser. Don't use them if you intend your site to work for the majority of Internet users.

Answer 4

The HTTP 1.1 specification says:

URIs in HTTP can be represented in absolute form or relative to some
known base URI [11], depending upon the context of their use. The two
forms are differentiated by the fact that absolute URIs always begin
with a scheme name followed by a colon. For definitive information on
URL syntax and semantics, see "Uniform Resource Identifiers (URI): Generic Syntax and Semantics," RFC 2396 [42] (which replaces RFCs 1738 [4] and RFC 1808 [11]). This specification adopts the definitions of "URI-reference", "absoluteURI", "relativeURI", "port",
"host","abs_path", "rel_path", and "authority" from that
specification.

The HTTP protocol does not place any a priori limit on the length of
a URI. Servers MUST be able to handle the URI of any resource they serve, and SHOULD be able to handle URIs of unbounded length if they provide GET-based forms that could generate such URIs.* A server SHOULD return 414 (Request-URI Too Long) status if a URI is longer than the server can handle (see section 10.4.15).

Note: Servers ought to be cautious about depending on URI lengths above 255 bytes, because some older client or proxy implementations might not properly support these lengths.

As mentioned by @Brian, the HTTP clients (e.g. browsers) may have their own limits, and HTTP servers will have different limits.

Answer 5

from link text "Maximum URL length is 2,083 characters in Internet Explorer"

A have problems with IE and urls longer than that. Firefox seems to work fine with >4k chars.

Answer 6

There is really no universal maximum URL length. The max length is determined only by what the client browser chooses to support, which varies widely. The 2,083 limit is only present in Internet Explorer (all versions up to 7.0). The max length in Firefox and Safari seems to be unlimited, although instability occurs with URLs reaching around 65,000 characters. Opera seems to have no max URL length whatsoever, and doesn't suffer instability at extremely long lengths.