# 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.


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# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.old-faithful.net/references/cid-lookup-api.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.