Specification

The Ambient Context Protocol lets a desktop app tell an ambient agent what the user is looking at, so that "this" means something when the user asks a question. It also lets the agent's interface appear beside the thing in question. An app answers two questions: what is open and selected, as one tree of elements, and where an element is on screen. Version 0.2.0 is defined as an extension to the Model Context Protocol (MCP): both answers are MCP resources.

Version 0.2.0 is the result of three accepted proposals: RFC-0001, the element model, RFC-0002, a provider on a listener the app already has and RFC-0003, a hovered state. Where this specification and an RFC differ, this specification is the contract and the difference is a defect to report.

Section numbers run through the whole specification, so "section 8" names the same thing wherever it is cited.

File	Sections
Overview	1. The problem · 2. An example · 3. Roles and principles
Operations	4. Operations: 4.1 current, 4.2 locate
Elements	5. Elements: 5.1 fields, 5.2 roles, 5.3 states, 5.4 ids and instances, 5.5 content, 5.6 attributes, 5.7 what to report
Locations	6. Locations
The MCP binding	7. The MCP binding: 7.1 the server, 7.2 declaring the extension, 7.3 the two resources, 7.4 errors and refusals, 7.5 an optional tool, 7.6 older MCP clients · 11. Implementing a provider · 14. MCP details this draft relies on
Discovery	8. Discovery
Rules	9. Rules: 9.1 for providers, 9.2 for hosts
Versioning	10. Versioning · 12. Not in version 0.2.0 · 13. Open questions · Changelog

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