# Retrosynthesis Engines

Pending AI offers a novel Deep-Learning MCTS **Retrosynthesis** platform for synthetic planning. An *engine* provides the underlying architecture and functional procedure used for building complex multi-step synthetic routes. When submitting a query molecule for assessing synthetic accessibility, an engine must be specified using its respective `id` field.

**Considerations**

* An engine requires significant computational resources affected by different parameters when completing a Retrosynthesis job. Large screening campaigns are queued onto identical engine instances, potentially leading to longer wait times for screening results.
* Engine selection can significantly impact the diversity of the generated synthetic routes. Try different engines to yield varied synthetic routes

See [here](https://docs.pending.ai/capabilities/synthetic-accessibility) for more information on our **Retrosynthesis** capability.

## List engines

> Retrieve a list of engines.

```json
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Try different engines to yield varied synthetic routes\n\nSee [here](https://docs.pending.ai/capabilities/synthetic-accessibility) \nfor more information on our **Retrosynthesis** capability.\n","name":"Engines"}],"servers":[{"description":"Pending AI Server","url":"https://api.pending.ai/retro/v2","variables":{"environment":{"default":"api","description":"The environment to use for the API.","enum":["api","api.dev","api.stage"]}}}],"security":[{"oauth":[""],"token":[""]}],"components":{"securitySchemes":{"oauth":{"description":"OAuth2 authentication.","flows":{"implicit":{"authorizationUrl":"https://auth.pending.ai/authorize","refreshUrl":"https://auth.pending.ai/oauth/token","scopes":{}}},"type":"oauth2"}},"schemas":{"EngineResource":{"description":"Engines are used when performing a retrosynthesis plan for a target\nmolecule. 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Refer to `error.details` to resolve individual errors. 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```