Why F# Breaks OpenAPI Routes: Sharp Symbols Clash With URL Fragment Rules

A developer building a music theory API found that entering F# as a root note in an OpenAPI interface produced a 404 error. The cause is that the # character marks a URL fragment, so the browser strips everything after it before the request reaches the server. Possible fixes such as percent-encoding, query parameters, or substituting letters were each judged to be awkward or musically misleading. The developer instead adopted German notation, which uses "is" for sharps and "es" for flats, such as Fis, so the URLs stay clean without special characters.