Quick wins for a faster PC:
Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Repair Windows errors before they cause bigger problemsFix Now →An agent can expose its own tools through an MCP server while using an MCP client to call other servers. This composition—often called the bidirectional MCP pattern—is an architectural choice, not a separate MCP role or a requirement for every agent. It lets another host invoke the agent’s capabilities while the agent coordinates downstream services behind that interface.
What “bidirectional MCP” means
MCP defines host, client, and server roles and a protocol for exchanging context and capabilities. The host is the AI application; it creates an MCP client for each server it connects to. An agent or service can therefore be a server on one connection and a client on another: upstream, it offers capabilities; downstream, it consumes capabilities offered elsewhere.
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The protocol standardizes the exchange, not the agent’s reasoning or orchestration strategy. As the MCP architecture overview puts it, “MCP focuses solely on the protocol for context exchange—it does not dictate how AI applications use LLMs or manage the provided context.” Combining roles is one way to build an application around that protocol.
How the pattern works
This is an illustrative architecture, not a mandatory protocol topology:
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- An upstream MCP host connects to the agent’s MCP server and discovers the tools or resources it exposes.
- The host calls one of those capabilities.
- The agent uses its MCP client to discover or call downstream MCP servers, then combines the returned information or actions into its response.
- If the operation needs user input, the server follows the input-request flow supported by the negotiated protocol revision; for revision
2026-07-28, that means returning an input-required result and allowing the client to gather input and retry the original call.
This arrangement is useful when reusable orchestration should sit behind a stable tool interface, or when a service needs to aggregate capabilities from several MCP servers. It does not automatically make reasoning better, calls faster, or the system more reliable or secure. Those outcomes depend on implementation choices such as tool selection, authorization, and failure handling.
“Bidirectional” does not mean every message is unsolicited
The term can refer broadly to exchanges in which messages travel in both directions, but the important version-sensitive case is a server that needs client or user input while work is underway. In protocol revision 2026-07-28, this is a multi-round-trip flow: a client-started operation receives an input-required result, the client mediates the response, and the original call is retried. It is not an unsolicited server-initiated JSON-RPC request in that revision. See the 2026-07-28 specification.
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Older examples may show server-initiated requests such as elicitation/create, sampling/createMessage, or roots/list. Do not copy them as if they applied to every revision. The TypeScript SDK migration guide describes how its newer implementation can fulfill embedded input requests through registered handlers and retry the call; check the guide and the SDK version used by your application: TypeScript SDK migration guide.
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Design each connection’s capabilities and trust boundary
Being a client and a server does not make the two connections interchangeable. Decide separately what the agent exposes upstream, what it may call downstream, and which identity and credentials apply to each side.
- Define the capability boundary. Expose only the tools or resources the upstream host needs. Limit downstream access to the MCP servers and operations the agent needs.
- Negotiate and inspect support. Participants negotiate a protocol version and advertise capabilities. Use only features supported by the counterpart and the negotiated revision; architecture guidance explains version and capability discovery at MCP architecture.
- Separate authorization paths. Authorization for an MCP client’s connection to an MCP server is distinct from a server obtaining authorization to a third-party service. Do not forward the client’s bearer token to a third party.
- Make failures attributable. Decide how to handle downstream timeouts, partial results, and retries, and preserve enough observability to identify which component initiated an action. MCP does not prescribe a single best failure-handling design.
Handle input and third-party credentials safely
For revision 2026-07-28, follow the multi-round-trip input-required pattern when a server needs client input during an operation. In the TypeScript SDK v2, consult the migration documentation for request-handler registration and the matching capability declaration. The guide also marks sampling and roots deprecated as of this revision, pointing developers instead toward direct provider APIs for sampling and paths or tool parameters, resource URIs, or configuration for roots. These details are SDK- and version-sensitive, so confirm them against the SDK actually in use.
Input mode matters when the request concerns third-party authorization. Form elicitation is for structured, non-sensitive input. URL mode can direct the user to an external site for sensitive interactions; it is for third-party authorization, not for authorizing the client’s MCP connection. The MCP server is responsible for storing and managing third-party tokens. Credentials should not pass through the MCP client or be returned to it. See the elicitation specification.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Keep protocol statelessness separate from application state
The 2026-07-28 release describes a stateless protocol core. An application that needs continuity between calls can mint an explicit handle and pass it back through tool arguments. This makes the application’s state explicit rather than assuming that the protocol itself provides it. User-bound credentials for external authorization are a separate matter and remain managed by the server.
Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsHow to evaluate an implementation
When comparing a single-role gateway with a composed client-and-server agent, assess the actual boundaries and behavior rather than treating “bidirectional” as a quality guarantee.
Quick Recap
| Evaluation area | Questions to ask |
|---|---|
| Capabilities | Which tools and resources are exposed upstream, and which downstream servers can the agent call? |
| Identity and authorization | Who authenticates to each server? How is user identity mapped, and where are third-party tokens held? |
| Protocol version and input | Which revision is negotiated, and is client input handled using that revision’s supported flow? |
| State and deployment | Is state carried in explicit handles or assumed to persist across calls? How does the chosen transport and hosting setup affect that choice? |
| Failures and observability | What happens on downstream timeouts or partial results, how are retries bounded, and can operators tell which component produced an action? |
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