MCP Protocol

Reference

Protocol surface that affects MCP governance and MCP client compatibility.

Supported protocol versions

AIControls supports MCP protocol version 2026-07-28 (and earlier revisions advertised by upstream servers).

tools/call result discriminator (resultType)

For MCP protocol version 2026-07-28 and later, tools/call responses include a resultType field.

resultType	Meaning
complete	The tool call is finished and no further client action is required.
input_required	The server is using the multi round-trip request protocol (MRTR / SEP-2322) and the client should fulfill inputRequests and retry, or retry later when load-shedding is indicated.

Notes:

• input_required results include inputRequests and may include an opaque requestState the client must echo back when retrying.
• An empty inputRequests object is meaningful: it indicates load-shedding (retry later).
• Requests carrying inputResponses or requestState bypass response-cache reads and writes.
• Upstream results with non-empty inputRequests and retries with non-empty inputResponses are rejected until governed MRTR fulfillment is implemented. They are not relayed to a downstream client's automatic sampling, elicitation, or roots handlers. Empty-map load-shedding remains supported.

Structured tool results

The proxy preserves upstream structuredContent alongside content for HTTP and stdio MCP servers. Numbers keep their exact upstream representation, including integers above 2^53 and decimals with more than 17 significant digits. SSE events at or near the 16 MiB per-event limit are passed through unchanged, and their numbers may be rounded. Response policies and content scanning inspect a JSON representation containing both fields. Redaction and tokenization apply to both representations; if a rewrite produces invalid JSON, the response is rejected rather than returning the original structured data. Text-only noise filtering, deduplication, and compression are skipped for structured results to preserve their schema.