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You might want to rewrite requests so they’re served by specific sections of your app without having to redirect users. For example, you might want to make URLs seem semantic to users without having to rewrite your app architecture. In such a case, you might want requests to /shoes/great-shoe/ to be served as if they were requests to /?category=shoes&product=great-shoe. If so, add a rule similar to the following:
.upsun/config.yaml
applications:
  myapp:
    source:
      root: "/"
    web:
      locations:
        '/':
          ...
          rules:
            '^/(?<category>[^/]+)/(?<product>[^/]+)/$':
              passthru: '/?category=$category&product=$product'
Or you might organize your images by file type, but don’t want to expose the organization externally. You could rewrite requests to do that behind the scenes:
.upsun/config.yaml
applications:
  myapp:
    source:
      root: "/"
    web:
      locations:
        '/':
          ...
          rules:
            '^/img/(?<name>.*)\.(?<type>.*)$':
              passthru: '/$type/$name.$type'
Now a request to /img/image.png returns the file found at /png/image.png.

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Query parameters

Query parameters in the request are untouched by rules and will be passed to the app. For example, if you have the category and product rule from previously, a request to /shoes/great-shoe/?product=terrible-shoe is rewritten to ?category=shoes&product=great-shoe&product=terrible-shoe. In that case, the product query parameter sent to the app will contain the value terrible-shoe.
Last modified on March 12, 2026