# Welcome to the Amazon Mechanical Turk Requester User Interface Guide
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Mechanical Turk is a web service that provides an on-demand, scalable, human workforce to complete tasks. The Amazon Mechanical Turk Requester User Interface (RUI) provides access to Mechanical Turk functionality using a graphical user interface. Mechanical Turk provides a marketplace for work and gives you access to Workers around the world and around the clock. Mechanical Turk enables you to complete a variety of tasks, including data categorization, moderation, verification, and tagging. For more information about Mechanical Turk, see [https://www.mturk.com](https://www.mturk.com).

Good workers and clear instructions are the key to obtaining successful results for any kind of project. Mechanical Turk provides tools to help you select good *Workers* and create clear instructions for the selected Workers. You can make your instructions as detailed as necessary to help Workers understand the tasks you want them to perform. 

You can choose to identify good Workers from the over 500,000 Workers in the Mechanical Turk Marketplace, or you can use Master Workers. *Master Workers* are Workers who have demonstrated the ability to provide successful results for specific types of tasks across multiple *Requesters* on the Mechanical Turk Marketplace. 

**Important**  
If you do not add a CORS configuration to the S3 buckets that contain your image input data, HITs that you create using those input images will fail. To learn more, see [CORS Configuration Requirement](https://docs.aws.amazon.com/AWSMechTurk/latest/AWSMechanicalTurkRequester/MturkCorsConfig.html).

## Advantages of Mechanical Turk
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The major advantages of Mechanical Turk include:
+ **On-demand workforce** – With 500,000 Workers in 190 countries around the world, Mechanical Turk Workers are available whenever you need them. 
+ **Scalable workforce** – With no minimum project size, you can scale your Mechanical Turk volume up and down with your business. You may have 100 tasks one day and 10,000 the next.
+ **Speed** – Workers can complete tasks in parallel so work is done faster with a limited workforce.
+ **Accuracy** – Master Workers have been pre-qualified for their demonstrated ability to follow instructions when completing tasks.
+ **Pay only for satisfactory work** – You do not pay a Worker or Mechanical Turk fees until you accept the Worker's work. 

## How do I...?
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|  How do I...? |  Relevant Topics  | 
| --- | --- | 
| Learn how Mechanical Turk works |  [Mechanical Turk concepts](mechanical-turk-concepts.md)  | 
| Create a Mechanical Turk Project |  [Create an Amazon Mechanical Turk project](CreatingYourBatchofHITs.md)  | 
| Publish a batch of Human Intelligence Tasks (HITs) |  [Publish a batch of HITs](PublishingYourBatchofHITs.md)  | 
| Manage a batch of HITs |  [Manage batches](ManagingYourHITs.md)  | 
| Manage Mechanical Turk Workers |  [Manage Workers](ManagingWorkers.md)  | 
| Manage Mechanical Turk Worker qualification types |  [Managing qualification types](ManagingQualificationTypes.md)  |