I'm building a music theory API. I typed F# as root note into the "tonic" interface, which OpenAPI translated into a URL and I got a subsequent 404. Everything broke. Here's what happened and how I created a work-around. What # means to a URL The # character is reserved in URLs to signal a fragment identifier. Everything after the # character is interpreted by the browser as an anchor on the page, not part of the path. So something like /scales/F#/major is parsed as /scales/F ...