Amazon Mechanical Turk
API Reference (API Version 2014-08-15)



Instead of providing a QuestionForm data structure that tells Amazon Mechanical Turk how to display your questions and collect answers, you can host the questions on your own website using an "external" question.

A HIT with an external question displays a web page from your website in a frame in the Worker's web browser. Your web page displays a form for the Worker to fill out and submit. The Worker submits results using your form, and your form submits the results back to Amazon Mechanical Turk. Using your website to display the form gives your website control over how the question appears and how answers are collected.

To use an external question with a HIT, you provide an ExternalQuestion data structure as the value of the Question parameter when calling the CreateHIT operation. As with the QuestionForm data structure, an ExternalQuestion is a string value that consists of XML data. This data must conform to the ExternalQuestion schema. See WSDL and Schema Locations for the location of this schema. For more information about using XML data as a parameter or return value, see Using XML Parameter Values.


You can only use an external question as the question of a HIT. You cannot use an external question with a Qualification test.

The ExternalQuestion data structure is a value in a HIT data structure.

All elements in a ExternalQuestion belong to a namespace whose name is identical to the URL of the ExternalQuestion schema document for the version of the API you are using.

The ExternalQuestion Data Structure

The ExternalQuestion data structure has a root element of ExternalQuestion.

The ExternalQuestion element contains the following elements:



The URL of your web form, to be displayed in a frame in the Worker's web browser. This URL must use the HTTPS protocol.

Type: URL

Default: None

Amazon Mechanical Turk appends the following parameters to this URL: assignmentId, hitId, turkSubmitTo, and workerId. For more information about these appended parameters, see the sections following this table.



The height of the frame, in pixels.

Type: Integer

Default: None



The following is an example of a complete ExternalQuestion data structure. Remember that to pass this structure in as the value of a parameter to an operation, XML characters must be escaped as character entities. For more information about escaping XML characters, see Using XML Parameter Values. For information on the ExternalQuestion schema URL, see WSDL and Schema Locations.

<ExternalQuestion xmlns="[the ExternalQuestion schema URL]">

The External Form

When a Worker attempts to complete a HIT with an external question, the external website is loaded into a frame in the middle of the screen. The web page at that URL should display a form for the Worker to fill out, and all the information the Worker will need to complete the HIT.

The Frame's URL and Parameters

The URL used for the frame is the ExternalURL of the question with the following parameters appended: assignmentId, hitId, turkSubmitTo, and workerId. These parameters are appended CGI-style: The full URL has a question mark (?) before the first parameter, and an ampersand (&) between each parameter, with each parameter consisting of a name, an equal sign (=), and a value. Other parameters already present in this style in ExternalURL are preserved, so the final URL will only have one question mark, and all parameters will be separated by ampersands (&).


The URL you use for the ExternalURL must use the HTTPS protocol.

For example, consider an ExternalURL of:

With this ExternalURL, the full URL used for the page in the frame could be as follows:

Preview Mode

Your external question will be displayed when a Worker previews the HIT on the Amazon Mechanical Turk website, before the Worker has clicked the "Accept HIT" button. When the HIT is being previewed, the URL will have a special value for the assignmentId: ASSIGNMENT_ID_NOT_AVAILABLE.

When a Worker previews a HIT, your web page should show her everything she will need to do to complete the HIT, so she can decide whether or not to accept it. The easiest way to do this is to simply display the form as it would appear when the HIT is accepted. However, you may want to take precautions to prevent a Worker from accidentally filling out or submitting your form prior to accepting the HIT.

You can use JavaScript or server-side logic to check the assignmentId parameter, and change the display of the form if the HIT is being previewed (assignmentId=ASSIGNMENT_ID_NOT_AVAILABLE).

If a Worker submits your form before accepting the HIT, and your form attempts to post the data back to Amazon Mechanical Turk, Amazon Mechanical Turk will display an error message to the Worker, and the results will not be accepted.

The Form Action

The form on the external website must post the result data back to Amazon Mechanical Turk using the following URL:

Or, if you are using the Amazon Mechanical Turk sandbox, you should post the result data back to Mechanical Turk using the following sandbox URL:

The form must include the assignmentId field that was appended to the URL used to access your form. It should be submitted along with the other form fields submitted by your form, with a name of assignmentId and the same value as was passed to the form. Be sure to spell the field name as it appears here, with the same letters uppercase and lowercase.


The field names assignmentId, hitId, turkSubmitTo, and workerId are reserved for special purposes. Your form only needs to submit the assignmentId field. Any data submitted with a field name of "hitId" will be ignored, and will not appear in the results data for the HIT.

The form must submit data to that URL using the "POST" method. The data the form submits should be name-value pairs in the CGI-style:

  • Each field appears as the name, an equal sign, and the value. For example: favoriteColor=blue

  • Data that appears in the posted URL is preceded by a question mark (?), and is delimited by ampersands (&). For example:
  • Data that appears in the HTTP message body (using the "POST" method) has one data pair per line. For example:


The easiest way to post the data in the CGI-style is to use an HTML form on the web page, with the externalSubmit URL as the "action," and "POST" as the "method."

The Answer Data

When the Worker submits your form, the form sends the field data to Amazon Mechanical Turk using the externalSubmit URL, and Amazon Mechanical Turk records the field data as the results of the Assignment.

When you retrieve the results using the GetAssignmentsForHIT operation, the field data submitted by your form will appear in the Answer of the Assignment as if each field were a free-text answer. The QuestionIdentifier element of the answer will be the name of the field, and the FreeText element will contain the value.

See the QuestionFormAnswers data format for more information about the format of answer data.

Guidelines For Using External Questions

External questions give your application a great deal of power over how Workers submit results for your HITs. To ensure you get good results for your HITs, you should make sure your web server and web pages can provide your Workers with a quality experience.

Because external questions depend on your web server for rendering the question form, both while Workers are previewing HITs and while Workers are completing HITs, your server will need to be engineered for high availability. The Amazon Mechanical Turk website gets heavy traffic, so your web server will need to be able to respond quickly and correctly when receiving many requests in a short period of time.


Amazon S3 offers high availability hosting of data, accessible via public URLs. You can host your external questions as web pages in Amazon S3, and not have to run your own high availability web server.

Your website can do many things inside the frame, but eventually it must cause the Worker's browser to load the "externalSubmit" URL in the frame with the results in POST data. The easiest way to do this is with an HTML form whose fields contain the HIT results, with a submit button that the Worker will click. If an external HIT prevents the Worker from submitting results back to Amazon Mechanical Turk using the "externalSubmit" mechanism, the Worker may not be able to claim rewards or continue doing work without restarting their session. Amazon Mechanical Turk reserves the right to remove any external HITs that are not functioning properly.


Your HIT will be rendered inside an IFRAME that has certain limitations. The IFRAME operates in HTML5 "sandbox" mode that has extra restrictions on the content that can appear in the frame. This limits your ability to execute certain code and to use technologies such as Adobe Flash. To ensure your HITs work as expected, we recommend you test them first in the Requester Sandbox.

Finally, please remember that external questions must meet the Amazon Mechanical Turk Participation Agreement, and Amazon Mechanical Turk's standards for appropriate content. Specifically, the Participation Agreement expressly prohibits the use of Amazon Mechanical Turk for advertising or solicitation. If your website typically displays advertising to visitors, please make sure those advertisements do not appear in your external questions. Amazon Mechanical Turk reserves the right to remove HITs with inappropriate content.