303

Why 303 is special

Same number, different meanings

How 303 is understood across different contexts — never implying one meaning because of another.

• Mathematics

  303 solves the double-submit problem. After a POST it tells the browser to fetch a different URL with GET, so refreshing the resulting page re-reads a receipt rather than re-placing an order. The pattern has a name — Post/Redirect/Get — and 303 is the status code that makes it correct rather than merely conventional.

• Technology & computing

  Refreshing a page after a form submission used to re-submit it. 303 fixes that: it tells the browser to fetch a different URL with GET regardless of the method just used, so the reload re-reads a confirmation rather than placing a second order. The pattern is standard enough to have a name.

• Media & popular culture

  The TB-303 was marketed as accompaniment for solo guitarists and failed at that completely. Its squelching filter, discovered by musicians who bought it cheap, is the defining sound of acid house.

Not just a mathematical number

303is also used in ways where ordinary arithmetic doesn't apply — each listed below with what genuinely does and doesn't follow from it.

• Mathematical number

  A genuine quantity — its mathematical properties (prime, square, factors, and so on) are real facts about it.

  A genuine quantity that ordinary arithmetic applies to — it can be prime, even, a perfect square, added to another number meaningfully, and so on.

• Code

  Also used as a code — HTTP status codes.

  An assigned identifier from a fixed registry or standard — its digits don't represent an amount, and arithmetic on it is meaningless (HTTP status 404 + 1 is not a 'better' status; it's a different, unrelated code).