MCP: versions, capabilities and security
Understand protocol evolution without conflating adoption with universal maturity.
The role of the protocol
MCP defines interactions between clients and servers exposing tools, resources and prompts. Its core uses structured messages; it does not guarantee tool safety or user consent for each action.
A dated 2026 release
The project announced a 28 July 2026 specification with a stateless core, new interaction patterns and extension and authorization improvements. Consult official release notes rather than mixing different protocol generations.
Capabilities must be negotiated
A capability in the specification does not imply implementation in every client or server. Inspect initialization, advertised capabilities, error messages and backward compatibility before claiming interoperability.
End-to-end security
Remote servers need proper resource identification and authorization validation. Distinguish least-privilege permissions, tokens intended for a particular server and reversible actions.
A version does not imply every capability
MCP defines core mechanisms and extensions adopted by different libraries at different speeds. During initialization, observe negotiated versions and advertised capabilities. A compatible library does not guarantee every new feature or correct behavior under errors and disconnections.
Compatibility test plan
Prepare a client and two servers with known versions and capabilities. Test tool listing, input validation, error responses, interrupts and authorization behavior. Record which features work for each combination and keep secret-free traces. Results describe tested versions, not every product.
Core steps
- 01Read the dated specification
- 02Check negotiated capabilities
- 03Test a real exchange
- 04Verify authorization scopes
Three questions to ask
Does MCP make all tools safe by default?
Does the client advertise the required feature?
Are tokens bound to their intended resource?
Read the source documents
Versions, reuse terms and document status can change. Check them on the original sites.