URI Template Expander (RFC 6570)

How to use

1. Enter a URI template using {braces}, e.g. {/path}{?query*}.
2. Provide the variables as a JSON object (strings, numbers, arrays, or objects).
3. Read the expanded URL and copy it; tweak the template or variables to see the result update live.

Frequently asked questions

What do the operators mean?

The first character inside the braces selects an operator: none = simple comma-joined values; `+` keeps reserved characters unescaped; `#` makes a fragment; `.` a label; `/` path segments; `;` path-style `;name=value` params; `?` a form query `?name=value`; `&` a query continuation. Each controls its own separator and whether names are included.

What do `*` and `:n` do?

`*` is the explode modifier: a list or map expands into separate components (e.g. `{?list*}` → `?list=a&list=b` instead of `?list=a,b`). `:n` is a prefix modifier that truncates a string value to the first n characters before encoding (e.g. `{var:3}` of `value` → `val`).

How do I pass lists and maps?

Use JSON: a list is an array (`"fields": ["name","email"]`) and an associative map is an object (`"keys": {"semi": ";"}`). Strings and numbers are scalars. A variable that's missing, null, an empty list, or an empty object is treated as undefined and contributes nothing to the output.

Is the encoding correct?

Yes — values are percent-encoded per the operator's allowed set. Simple and most operators encode everything outside the unreserved set, while `+` and `#` also pass reserved URL characters (and existing %XX triples) through unescaped, matching RFC 6570. The implementation passes the spec's full example table.

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