> 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/references/cid-lookup-api.md).

# CID Lookup API

{% hint style="info" %}
Support for these endpoints is currently in progress.
{% endhint %}

You can look up CIDs for individual slots or transactions by using our hosted service:

* **Transaction signatures**: **`https://cid.old-faithful.net/api/v1/sig-to-cid/<sig>`**
* **Blocks**: **`https://cid.old-faithful.net/api/v1/slot-to-cid/<slot>`**

If the CID is available, the API will return the CID for the block or transaction.

A HTTP 404 response indicates the transaction or slot is unavailable in Old Faithful.