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Defined in: client/client.ts:74

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Properties

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auth?

Defined in: client/client.ts:79 Authentication to attach to HTTP requests. A plain string is treated as a Bearer token.

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autoInitialize?

Defined in: client/client.ts:91 When true (default), the MCP initialize handshake is performed automatically inside connect().

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cachePartition?

Defined in: client/client.ts:145 Opaque per-principal identifier for response-cache writes whose server-reported cacheScope is 'private'. Set this to a stable identity of the authorization context (e.g. the auth subject) when one responseCacheStore backs several principals. Passed through verbatim.

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defaultCacheTtlMs?

Defined in: client/client.ts:151 TTL (ms) applied when a cacheable result arrives without a ttlMs field. Default 0 (never served from cache, but still stored). Passed through verbatim.

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defaultOptions?

Defined in: client/client.ts:92

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handlers?

Defined in: client/client.ts:80

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inputRequired?

Defined in: client/client.ts:131 Multi-round-trip auto-fulfilment (protocol revision 2026-07-28). On the modern era, servers obtain client input (elicitation, sampling, roots) by answering a request with an input_required result instead of a server→client request. By default the client fulfils these automatically through the same handlers.sampling/handlers.elicitation callbacks, retrying up to maxRounds times. Set autoFulfill: false for manual mode. Has no effect on legacy-era connections. Passed through verbatim to the SDK client.

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legacySSE?

Defined in: client/client.ts:159 Allow the deprecated SSE transport when a target URL’s path indicates SSE (e.g. ends in /sse). Default false — such URLs throw a clear error pointing at Streamable HTTP and this flag, rather than silently connecting over a transport the MCP SDK itself marks @deprecated. When enabled, a one-time deprecation warning is logged via console.warn.

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prior?

Defined in: client/client.ts:120 A cached era verdict from a previous connection to the same server, so connect() can skip the server/discover probe entirely. Takes precedence over versionNegotiation. { kind: 'modern', discover } adopts a prior DiscoverResult with zero round trips; { kind: 'legacy' } skips the probe and runs the plain legacy initialize handshake. Freshness is the caller’s responsibility — a stale modern verdict fails loudly at the first request; a stale legacy verdict succeeds silently forever. Reuse only within one authorization context.

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responseCacheStore?

Defined in: client/client.ts:138 The response-cache store backing cacheable results (SEP-2549 ttlMs/ cacheScope hints on listTools/listResources/listResourceTemplates/ listPrompts/readResource). Defaults to a fresh in-memory store per client (the SDK’s own default) when omitted. Passed through verbatim.

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roots?

Defined in: client/client.ts:86 Filesystem roots to advertise to the server. Accepts a static array of strings / Root objects, or an async callback invoked on each roots/list request (useful for dynamic root sets).

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versionNegotiation?

Defined in: client/client.ts:109 Protocol version negotiation (protocol revision 2026-07-28 and later). The default is { mode: 'auto' }: connect() probes the server once with server/discover and uses the modern (2026-07-28) era on definitive modern evidence, falling back to the plain legacy initialize handshake on anything else (a method-not-found answer, silence on a local stdio pipe, a probe child that exits). The probe is stall-safe in the SDK: on stdio it runs against a short-lived sibling process and a timeout falls back to legacy, while on HTTP — where silence means an outage — a probe timeout rejects with a typed error instead of hanging. Pass { mode: 'legacy' } to opt out: no probe, the 2025 sequence byte-identical to prior behavior. Pass { mode: { pin: '2026-07-28' } } to require the modern era outright — connect() throws if the server cannot speak it. See getProtocolEra() to read the negotiated result after connecting.