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Validator.nu Web Service Interface

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Revision as of 10:13, 18 August 2008 by Hsivonen (talk | contribs) (→‎Sample Messages: Precise error)
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Validator.nu can be called as a Web service. Input and output modes can be chosen completely orthogonally. Responses and requests can be optionally compressed (independently of each other).

(Please use the Web service API reasonably. See the Terms of Service.)

Input Modes

For most Web service use cases, you should probably POST the document as the HTTP entity body.


Not Implemented

  • Document in a data: URI as a GET parameter.
  • application/x-www-form-urlencoded

Output Modes

When using Validator.nu as a Web service back end, the XML and JSON output formats are recommended for forward compatibility. The available JSON tooling probably makes consuming JSON easier. The XML format contains XHTML elaborations that are not available in JSON. Both formats are streaming, but streaming XML parsers are more readily available. XML cannot represent some input strings faithfully.


  • HTML with microformat-style class annotations (default output; should not be assumed to be forward-compatibly stable).
  • XHTML with microformat-style class annotations (append &out=xhtml to URL; should not be assumed to be forward-compatibly stable).
  • XML (append &out=xml to URL).
  • JSON (append &out=json to URL).
  • GNU error format (append &out=gnu to URL).
  • Human-readably plain text (append &out=text to URL; should not be assumed to be forward-compatibly stable for machine parsing—use the GNU format for that).

Not Implemented

  • Relaxed-compatible (lacks a spec)
  • Unicorn-compatible (hoping that Unicorn changes instead)
  • W3C Validator-compatible SOAP (legacy)
  • EARL (not implemented; domain modeling mismatch)


Validator.nu supports compression in order to save bandwidth.

Request Compression

Validator.nu supports HTTP request compression. To use it, compress the request entity body using gzip and specify Content-Encoding: gzip as a request header.

Response Compression

Validator.nu supports HTTP response compression. Please use it. Response compression is orthogonal to the input methods and output formats.

The standard HTTP gzip mechanism is used. To indicated that you prepared to handle gzipped responses, include the Accept-Encoding: gzip request header. When the header is present, Validator.nu will gzip compress the response. You should also be prepared to receive an uncompressed, though, since in the future it may make sense to turn off compression under heavy CPU load.

Sample Code

There a sample Python program that shows how to deal with compression and redirects. (It may not be exemplary Python, though.)

Sample Messages

There are documents for provoking different message types.

Error (precise location) HTML XHTML XML JSON GNU Text