# Clusters

A **cluster** is a set of unique domain names, saved under your account. It is what turns a search - which answers a question once, right now - into something you can keep, compare against next month's answer, combine with another, and read fields out of.

Clusters are for signed-in accounts. What one may hold depends on the plan; see [limits](https://publicwww.com/docs/clusters/limits/). The same clusters can be managed from code through the [API](https://publicwww.com/docs/api/clusters/), and by an AI assistant through the [MCP tools](https://publicwww.com/docs/mcp/tools/).

## What they are for

[**Keep** Store what a query returned. The index moves on and a search cannot be re-run against how it used to be.](https://publicwww.com/docs/clusters/creating/) [**Compare** Subtract one cluster from another to see who adopted a signature since last time, and who dropped it.](https://publicwww.com/docs/clusters/creating/) [**Combine** AND, OR and subtraction between clusters, saved as a new one.](https://publicwww.com/docs/clusters/creating/) [**Extract** Pull phone numbers, accounts or addresses off every site in the set, internal pages included.](https://publicwww.com/docs/clusters/extraction/) [**Filter** Upload your own list of domains and use it to narrow search results to it - or to everything but it.](https://publicwww.com/docs/clusters/creating/) [**Download** Browse page by page, or take the whole thing as a file.](https://publicwww.com/docs/clusters/creating/)

## In detail

- [Creating a cluster](https://publicwww.com/docs/clusters/creating/) - from search results, from a file, or from other clusters.
- [Extraction](https://publicwww.com/docs/clusters/extraction/) - reading fields off the sites in a cluster.
- [Limits](https://publicwww.com/docs/clusters/limits/) - how many, how large, and how extraction is counted.

## Worked examples

- [Tracking a widget change](https://publicwww.com/docs/clusters/example-widgets/) - which sites replaced one share widget with another, using two clusters and a subtraction across a PublicWWW update.
- [Extracting phones and emails](https://publicwww.com/docs/clusters/example-contacts/) - from two searches to a spreadsheet of contact details for Greek WordPress sites.

Source: https://publicwww.com/docs/clusters/