The limit is dependent on both the server and the client used (and if applicable, also the proxy the server or the client is using).
On servers, the industry practice by most CDNs is to have the limit at 8192 bytes.
On browsers, it varies.
The HTTP 1.1 specs section 3.2.1 provide warning on this topic,
Note: Servers ought to be cautious about depending on URI lengths |
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Good response on maximum http request - https://stackoverflow.com/questions/2659952/maximum-length-of-http-get-request