URI Template Builder (RFC 6570)

A URI Template describes a family of addresses with markers in braces, and RFC 6570 defines exactly how each marker expands. It is what the GitHub API returns in its link fields, and what lets a client assemble the right URL without concatenating strings. The page expands the template with the values you supply, applying each operator's encoding rules.

The difference that matters most is between the plain marker and the plus operator. The plain one encodes reserved characters, so a slash inside the value becomes its percent-encoded form and does not separate path segments. The plus one preserves reserved characters, which suits a variable holding a whole path. Confusing the two is the source of broken URLs or, worse, path traversal when the value comes from a user.

The other six operators add punctuation automatically: dot for a label, slash for a path segment, semicolon for a path parameter, question mark to open the query, ampersand to continue it, and hash for a fragment. Each knows which separator to use between values and whether to write the variable name — and that is exactly what saves assembling the URL by hand.