> For the complete documentation index, see [llms.txt](https://docs.pending.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.pending.ai/api-reference/pai-retro/building-block-libraries.md).

# Building Block Libraries

Explore the various libraries available for retrosynthesis

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 Library resources using offset-based pagination.\
> See the returned \`data\` field for more information about the Library\
> resources. Use additional \`metadata\` and \`links\` fields to navigate\
> the paginated resources.

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```