Connect your AI tools to Builder Fusion using the Model Context Protocol (MCP), an open standard that lets AI clients create and iterate on projects, inspect work, and use your design systems.
Note: The Fusion MCP server operates on the Fusion projects, branches, and design systems in the organization you select during authentication.
- The server uses streamable HTTP at
https://mcp.builder.io/mcp/fusion. - Authentication uses OAuth 2.0. Your MCP client opens Builder so you can sign in and select an organization.
- Fusion agent work runs asynchronously. Start a run, then check its status until it completes or fails.
- The server can create a project, iterate on an existing project, or continue work on a specific branch.
Access the Fusion MCP server from any MCP-compatible client, including AI coding assistants, IDE extensions, and LLM-based tools.
The Fusion MCP server uses OAuth 2.0 with dynamic client registration. The first time you use the server, your client opens a browser and redirects you to Builder. Sign in and select the organization that contains the Fusion projects you want to access.
Your client stores the resulting authorization and uses it for later requests.
Most MCP clients use a JSON configuration file to define connections. Add an entry for the Fusion MCP server using the following details:
- Server type: streamable HTTP
- Endpoint URL:
https://mcp.builder.io/mcp/fusion
Example configuration:
{
"mcpServers": {
"builder-fusion": {
"url": "https://mcp.builder.io/mcp/fusion",
"transport": "http"
}
}
}Consult your MCP client's documentation for the configuration file location and client-specific settings.
Add the following to your claude_desktop_config.json file:
{
"mcpServers": {
"builder-fusion": {
"url": "https://mcp.builder.io/mcp/fusion",
"transport": "http"
}
}
}Add the following to your MCP configuration file:
{
"mcpServers": {
"builder-fusion": {
"url": "https://mcp.builder.io/mcp/fusion",
"tools": ["*"]
}
}
}After connecting, test the server with prompts such as:
- Which Builder organization am I connected to?
- Show me my most recently updated Fusion projects.
- What Fusion branches am I currently working on?
- Which design systems are available?
After a successful connection, your client retrieves and displays information from your Fusion organization.
The Fusion MCP server provides tools for starting agent work, monitoring runs, finding projects and branches, reviewing prior prompts, and grounding generation in your design systems.
Start a Fusion agent run with a natural-language prompt. Omit a project ID to create a new project, or provide one to iterate on an existing project. Provide both a project ID and branch name to continue that branch instead of creating a new one.
You can include file attachments and other context. An optional idempotency key prevents a repeated request from starting a second run. The tool returns a run ID immediately so your client can monitor the asynchronous work.
Example Prompt
Get the latest snapshot for a run by its run ID. A run can be submitted, working, completed, or failed. Completed runs include a preview URL when available, and failed runs include error details.
Check the run periodically until it reaches a completed or failed state.
Example Prompt
List Fusion projects in the authenticated organization, ordered by most recently updated. Filter projects by a case-insensitive name search.
Results are paginated. Set a limit and offset, or use the next offset returned by the previous request, to retrieve more projects.
Example Prompt
Retrieve one project by its project ID. The result includes the project name, Builder editor URL, screenshot, and main branch information.
Use this after listing projects when you need enough context to choose a project or open it in Builder.
Example Prompt
List branches in a project so you can choose work to inspect or continue. Search across branch names, friendly names, descriptions, categories, Git branches, and other branch metadata.
Set createdByMe to show only branches created by the authenticated user. When createdByMe is true, you can omit the project ID to find your active work across the organization.
Example Prompt
Retrieve one branch by its project ID and branch name. The result includes the branch name, friendly name, and Builder editor URL.
Use this when you know which branch you want to inspect or continue.
Example Prompt
Review the user prompts and messages previously sent to a branch, ordered from oldest to newest. Use this context to understand what the branch is intended to do before asking the Fusion agent to continue it.
The default limit is 50 messages and the maximum is 200. When older messages are truncated, the first message remains available for context.
Example Prompt
List the design systems available in the authenticated organization. Your AI client can use these results to identify the components and design guidance that should ground a Fusion agent run.
Mention the relevant design system in your build prompt when you want the generated UI to follow it.
Example Prompt
Return the authenticated user's details and the organization to which the current token is scoped. Each token is scoped to exactly one organization.
Use this before starting work to confirm your AI client is connected to the intended Builder account and organization.
Example Prompt
For a new project, ask your client to list available design systems, then start a Fusion agent run without a project ID. Check the run until it completes and open the returned preview.
To continue existing work, use the project and branch tools to find the correct branch. Read its message history for context, then start a run with both the project ID and branch name. Check the new run until it completes.
Example Prompt