FeatureSets — Permission Control

FeatureSets are permission bundles that control what MCP capabilities (tools, resources, and prompts) each AI client can access. They let you grant fine-grained permissions per client, per Space.

Why FeatureSets

Without permission control, every AI client connected through the gateway can access every tool from every server. This creates risks:

• A junior developer's client could access destructive database tools
• An experimental AI agent could call deployment tools
• A read-only analysis tool could accidentally modify production data

FeatureSets solve this by letting you define exactly what each client can do.

FeatureSet Types

McpMux creates and manages four types of FeatureSets:

All

Grants access to every tool, resource, and prompt from every connected server in the Space. Use this for fully trusted clients.

Default

Automatically granted to all clients in the Space. Define a baseline set of capabilities that every client gets. You can still add more FeatureSets on top for specific clients.

ServerAll

Automatically created when a server first connects. Grants access to all features from that specific server. For example, when you enable the GitHub server, McpMux creates a "GitHub — All" FeatureSet containing all of GitHub's tools and resources.

Custom

User-defined FeatureSets with manually selected features. This is where you build your own permission bundles.

Include and Exclude

Each FeatureSet member can be set to include or exclude mode:

• Include — add this tool/resource/prompt to the set
• Exclude — remove this tool/resource/prompt from the set

Exclude rules always win over include rules. This means you can create a permissive base and then remove specific dangerous tools:

Example: "All GitHub except delete operations"

1. Include the GitHub — All ServerAll FeatureSet
2. Exclude delete_repository, delete_branch, delete_file

Composition

FeatureSets can contain other FeatureSets. This lets you build hierarchical permission structures:

• "Read Only" = Include tools that only read data from multiple servers
• "Android Development" = Include "GitHub — All" + "Firebase — All" + specific Gradle tools
• "Senior Developer" = Include "All" but exclude deployment and infrastructure tools
• "Intern" = Include "Read Only" + specific write tools for their assigned project

Common Use Cases

Role-Based Access

Domain Bundles

Safety Limits

Managing FeatureSets

Creating a Custom FeatureSet

1. Go to the FeatureSets page
2. Click Create FeatureSet
3. Give it a name and optional description
4. Add members — select features or other FeatureSets
5. Set each member to include or exclude mode

Putting a FeatureSet to work

A FeatureSet becomes a session's toolset when a folder routes to it — map the folder in the Workspaces tab (or let the AI pin it with Tool Optimization). Sessions whose folder isn't mapped fall back to the active Space's FeatureSet.

The effective toolset is the combination of the resolved FeatureSet(s), with exclude rules taking priority. McpMux shows exactly what resolves:

Next Steps

• Set up Clients and assign FeatureSets per Space
• Learn about Spaces for environment isolation
• Understand the Gateway to see how permissions are enforced at request time