MCP

UXC supports MCP servers over Streamable HTTP and stdio while preserving compatibility across the stateful and stateless protocol eras.

Version Support

Protocol	HTTP	stdio	Lifecycle
`2026-07-28`	Supported	Supported	Stateless requests with `server/discover` and per-request metadata
`2024-11-05`	Supported	Supported	Legacy `initialize` / `notifications/initialized` session
Legacy HTTP+SSE	Supported	Not applicable	Existing SSE endpoint and session behavior

UXC probes the server and selects the modern or legacy path automatically. Modern HTTP requests do not send Mcp-Session-Id and do not open a separate GET event stream.

Feature Matrix

Capability	`2026-07-28`	Legacy
Tools list and call	Supported	Supported
Resources list and read	Supported	Supported
Prompts list and get	Supported	Supported
Pagination and cache hints	Supported	Existing UXC cache policy
Custom MCP request headers	Supported	Not injected into legacy requests
`subscriptions/listen`	Supported through daemon-backed flows	Legacy resource subscriptions retained
Multi-round tool results	Explicit capabilities and continuation input	Results normalized as complete
OAuth for MCP HTTP	Supported	Supported

Stateless Request Metadata

For 2026-07-28, UXC sends the negotiated protocol version in both:

MCP-Protocol-Version
params._meta["io.modelcontextprotocol/protocolVersion"]

Each request also includes client information and client capabilities. UXC declares only capabilities supplied by the caller instead of claiming roots, sampling, or elicitation support by default.

Multi-Round Tool Results

UXC returns input_required results without automatically invoking a model or prompting a user. Callers can explicitly provide:

uxc --mcp-capabilities @capabilities.json <endpoint> <tool> ...
uxc --mcp-continuation @continuation.json <endpoint> <tool> ...

Continuation state is treated as opaque protocol data.

Subscriptions

Modern servers use the long-lived subscriptions/listen request. UXC keeps that request open through the daemon, filters notifications by subscription ID, and reopens it after a transport disconnect. It does not use Last-Event-ID or protocol session resumption for modern subscriptions.

OAuth Security

Authorization-code callbacks accept the RFC 9207 iss parameter. When it is present, UXC requires an exact match with the discovered issuer; callbacks without iss remain compatible with providers that do not advertise it.

Clients created through Dynamic Client Registration are bound to the issuer that registered them and are not reused after an issuer change. Client ID Metadata Documents are not implemented yet; RFC 7591 registration remains the fallback when no client ID is provided.

Migration from Legacy MCP

Server operators migrating to 2026-07-28 should expect:

server/discover instead of initialize.
Protocol and capability metadata on every request.
Independent HTTP POST requests without Mcp-Session-Id.
Request-scoped SSE only when a request streams.
subscriptions/listen instead of resource subscribe/unsubscribe methods.

UXC keeps the 2024-11-05 path for existing servers, so users do not need to change commands when a server upgrades.

Optional Extensions

UXC does not currently implement Tasks, Client ID Metadata Documents, or automatic roots, sampling, and elicitation providers. Unknown metadata and extension fields are preserved where the CLI contract permits.