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Caching

Caching hints belong to protocol revision 2026-07-28; see Protocol versions. A handshake-era client is served by the same server and simply never sees them.

server/discover, the four list methods and resources/read must carry ttlMs and cacheScope. The default is ttlMs: 0, cacheScope: "private" — conformant, and a flat refusal to let anything be cached. Say what you actually mean:

use Mcp\Schema\Enum\CacheScope;
use Mcp\Server\Wire\CachePolicy;

->setCachePolicy(
    CachePolicy::default(30_000)
        ->withMethod('tools/list', 3_600_000, CacheScope::Public)
        ->withMethod('server/discover', 3_600_000, CacheScope::Public),
)

public lets a shared proxy serve one caller's answer to another, so use it only for results that do not vary by caller. Only the operator can make that call, which is why the conservative default stands until you change it.

A ReadResourceResult may set its own ttlMs/cacheScope, which win over the policy.

Results produced by an MRTR retry are never given hints: their inputs are not part of any cache key.