# Building Block Libraries

For planning valid multi-step synthetic routes, various *building block libraries* are used to facilitate terminating different reaction subtrees. Our **Retrosynthesis** platform allows users to specify specific libraries for synthetic planning although it is recommended to select all libraries to improve the overall success rate. When submitting a query molecule for assessing synthetic accessibility, a list of libraries must be specified using respective `id` fields.

**Considerations**

* Library selection can influence the success of the retrosynthesis process. It's important to choose libraries that are well-suited for the specific synthetic routes.
* Some libraries may have limitations in terms of the reactions they can support or the average cost of available molecules. Use the latest libraries for optimal results (refer to the `available_from` field).

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

## List libraries

> Retrieve a list of libraries.

```json
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Use the latest libraries for optimal results (refer\nto the `available_from` field).\n\nSee [here](https://docs.pending.ai/capabilities/synthetic-accessibility)\nfor more information on our **Retrosynthesis** capability.\n                ","name":"Libraries"}],"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":{"LibraryResource":{"description":"Libraries contain large collections of building blocks that can be\nused to construct computed synthetic routes. 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```