modelcontextprotocol / modelcontextprotocol/ext-apps

SEP: Sandbox capabilities

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#58 3 comments 2 reactions 1 assignee View on GitHub

@idosal is already working on this.

Since Dec 1, 2025.

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Description

Currently, the SEP sets the minimum required permissions for the app runtime (allow-scripts allow-same-origin). However, it doesn't address -

  1. Additional capabilities like camera and microphone (@yannj-fr and others)
  2. Hardening like base-uri (which can affect capabilities like translations between web apps and raw HTML) or nested iframes (which might also require ui: csp: frameDomains).

These can fundamentally alter the content the server chooses to advertise or return.

We need to define the negotiation for these capabilities.

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