Where to find knowledge bases for ChatGPT and Claude

The fastest place to find a ready-made knowledge base that works in both ChatGPT and Claude is a marketplace built for it, which is what KBrain is: expert-built brains you can subscribe to and query over a single connection. Where you look after that depends on one question, whether you want prebuilt expertise you can plug in today, or you want to build a knowledge base from your own documents. There are five real places to find one, and they split cleanly along that line.

1. The KBrain marketplace: prebuilt brains for both assistants

KBrain is a marketplace of knowledge brains built by domain experts, each exposed as a queryable endpoint over MCP. You subscribe to a brain, connect KBrain once, and query it from ChatGPT, Claude, or any MCP-compatible assistant. Because the connection is external, one setup covers every brain you subscribe to and the same knowledge works across assistants instead of being trapped in one. You can also build a private brain from your own documents and keep it internal, or publish it. This is the only option on this list that gives you expertise you did not already have in-house, ready to query without building anything.

2. The ChatGPT custom GPT store

The custom GPT store is where you find GPTs that others have built, some of which attach a fixed set of files and retrieve from them. It is a genuine option if you live entirely in ChatGPT and want a prebuilt assistant around a topic. The limits are that the knowledge is locked to ChatGPT, you cannot reuse it in Claude, and you are trusting whatever files the creator attached, which you cannot see or update.

3. Claude Projects and connectors

Claude does not have a public store of prebuilt knowledge bases. Instead you build your own: a Project with attached files, or a connector that queries an external source over MCP. This is a build-your-own path, not a find-one path. It is a good fit when the knowledge is your own documents and you work mainly in Claude, though attached files are bound by the context window and do not travel to other assistants.

4. Your own files, Google Drive, and Notion

Often the knowledge base you want already exists as your own documents: a drive folder, a wiki, a Notion workspace. These become a real knowledge base once they are connected to an assistant and made queryable, which is exactly what an MCP connection does. KBrain can turn a document set or a synced Google Drive folder into a private brain queryable from ChatGPT and Claude, so your own material becomes a knowledge base without you moving it anywhere.

5. Public datasets and open data

Public datasets, open-data portals, and reference corpora are where you find raw subject-matter content. They are a source, not a knowledge base. An assistant cannot query a spreadsheet or a data dump directly with any precision until it has been chunked, indexed, and exposed for retrieval. Treat these as raw material you feed into one of the options above, not as something you connect directly.

How to choose

If you want expertise you do not already have, a specialist domain, a regulatory area, a technical niche, start at a marketplace and subscribe to a brain. If the knowledge is your own documents and you want it in both ChatGPT and Claude, connect it as a brain over MCP so you build it once. If you only ever use one assistant and have a small, stable set of files, the native option, a custom GPT or a Claude Project, is a reasonable shortcut. Raw datasets are input for any of these, not a destination.

The practical takeaway

There are five places to find a knowledge base for ChatGPT and Claude, but only one gives you prebuilt expert knowledge that works in both without building or hosting anything. That is what a marketplace like KBrain is for. Start there if you want a working knowledge base today, and build your own brain from your documents when the knowledge you need is already yours.