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A clone of better_errors for Clack.

By default, when Clack throws an exception when rendering a page, the server waits for the response until it times out while the exception waits in the REPL. This isn't very useful. So now there's this.



  (funcall clack-errors:*clack-error-middleware*
           :debug t)
  :port 8000)))

will wrap your Clack up in the clack-errors middleware, start the server and return a handler object.

By default, the middleware will show all information. In a production environment, you'll want to initialize this with the :debug parameter set to NIL.

Using a Custom Error Page

The middleware can be initialized with the :fn slot set to a lambda that takes a condition as its argument and returns the HTML string to return to the client.

  (funcall clack-errors:*clack-error-middleware*
    :fn (lambda (condition) "500 Internal Server Error")))


Copyright (c) 2013-2016 Fernando Borretti (

Licensed under the LLGPL License.