> For the complete documentation index, see [llms.txt](https://docs.old-faithful.net/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.old-faithful.net/introduction/architecture/indexes.md).

# Indexes

Indexes are needed to map Solana’s block numbers, transaction signatures, and addresses to their respective Content Identifiers. These indexes have been developed as part of this project. There are four content identifier indexes that the Old Faithful index generation can provide:

* **slot-to-cid**: Lookup a CID based on a slot number
* **tx-to-cid:** Lookup a CID based on a transaction signature
* **cid-to-offset-and-size**: Index for a specific CAR file, used by the local RPC server (see above) to find CIDs in a car file
* **sig-exists**: Index to check whether a specific signature exists in an epoch.

In addition, Old Faithful supports an index  `gsfa` that maps Solana addresses to a list of transaction signatures. This allows Old Faithful to support “Get Signatures For Address.”