# Welcome to the Amazon Mechanical Turk Requester User Interface Guide
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
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...?
| 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) |
# Mechanical Turk concepts
This section describes the concepts and terminology that you need to understand to use Amazon Mechanical Turk effectively.
## Requesters
A *Requester* creates tasks in Mechanical Turk for Workers to work on. As a Requester, you use the Requester User Interface (RUI) to create tasks, check the status of your tasks, and accept or reject work performed on tasks. Workers see your account name (specified by your Amazon.com account) when they view and accept your tasks.
## Human Intelligence Tasks (HITs)
A Human Intelligence Task (HIT) is a single, self-contained task a Requester creates on Mechanical Turk (for example, Identify the color of the car in the photo).
## Assignment
You can assign many Workers to work on the same HIT, which is an effective way to achieve consensus on a subject when many workers provide the same answer. A Worker can only accept a HIT once and can only submit one assignment per HIT. This guarantees that multiple Workers must complete a HIT that has multiple assignments.
If a Worker fails to complete an assignment before the time frame specified (that is, the Worker abandons the HIT), or if the Worker chooses not to complete it after accepting it (that is, the Worker returns the HIT), the assignment becomes available for other Workers to work on.
## Workers
A Worker is a person who completes assignments. Workers use the Mechanical Turk website ([http://mturk.amazon.com/](http://mturk.amazon.com/)) to find assignments to work on, submit responses, and manage their account.
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.
## Approval and payment
Workers submit responses for assignments. If you approve their work, Mechanical Turk transfers the HIT reward from your Mechanical Turk account to their Amazon Payments accounts. Workers don't get paid if you reject their work.
When you post a batch of HITs, you agree to approve or reject work by a specified deadline. If that deadline passes, Mechanical Turk approves the assignments and pays the Workers who submitted work.
Amazon Mechanical Turk processes payment of the reward to the Worker after you approve the assignment. Mechanical Turk transfers the reward from your Amazon.com account to the Worker's Amazon.com account. Before you can post your batch of HITs, you must have enough money in your account to pay for all of the work. You can deposit or withdraw funds from your Mechanical Turk account at any time using the Requester website ([http://requester.mturk.amazon.com/](http://requester.mturk.amazon.com/)).
## Qualification type
It is important to note that ***anyone*** can register to work in the Mechanical Turk Marketplace. To control who can work on ***your HITs***, you can require that Workers have specific qualifications before they can work on your HITs. You can create your own custom Qualification Types and assign them to Workers. Or, you can use the Qualification Types provided by Mechanical Turk.
Mechanical Turk provides several Qualification Types including Approval Rate, which is the percentage of assignments submitted that have been approved, and Assignments Approved, which is the number of Assignments that were approved for the Worker. The Approval Rate and Assignments Approve Qualification Types are automatically calculated based on a Worker's account statistics and history. If you don't want to use Workers who just registered this morning and have no work history, we recommend that you require Workers to have a 95% Approval Rate and 1,000 Approved Assignments to work on your project.
The **Master** Qualification Types give you easy access to Master Workers who have demonstrated the ability to provide successful results for specific types of tasks across multiple Requesters on the Mechanical Turk Marketplace.