An AI harness is the app or platform that you use to work with a Large Language Model (LLM). Claude Desktop, ChatGPT and Microsoft Copilot are examples of AI harnesses.
The model and the harness
An LLM, such as Claude, GPT or Gemini, only reads text and writes text. By itself, it cannot search the internet, open a file or get your production data.
The harness gives the model access to tools. The harness also controls how you talk to the model and what the model is permitted to do.
| Model | Harness | |
|---|---|---|
| What it is | The AI that reads and writes text | The app around the model |
| Examples | Claude Opus, OpenAI GPT-5, Gemini Flash 3.8 | Claude Desktop, Claude Cowork, ChatGPT, Microsoft Copilot, Google Antigravity 2.0 |
| What it does | Understands your question and writes an answer | Connects the model to tools, files, connectors and schedules |
What a harness gives the model
A harness can give the model:
- Connectors (MCP servers): access to data in other systems, such as Factbird, your ERP system or your email.
- Files: the ability to read your documents and create new ones, such as Excel files or PowerPoint presentations.
- Web search: access to information on the internet.
- Scheduled tasks: the ability to run a prompt automatically at a set time.
- Charts and interactive views: some harnesses support MCP-UI, which shows Factbird-native charts in the chat.
- Permissions: rules about what the model can do without asking you first.
Each harness gives a different set of these features. For example, scheduled tasks are available in Claude Cowork and ChatGPT, but not in normal Claude chat.
Why this matters for the Factbird MCP
The Factbird MCP is a connector. You add it to your harness, and the harness lets the model use it to query your Factbird data.
- The same model can give a different experience in different harnesses.
- Your harness, not Factbird, decides which features you get, such as scheduled tasks, file creation or charts.
- Your agreement with the harness provider controls how your data is stored and used after it leaves Factbird.
- You are not limited to Claude, ChatGPT and Microsoft Copilot. The Factbird MCP works with any harness that supports remote MCP servers with OAuth sign-in through CIMD or DCR.