Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries the full burden and does add genuine behavioral context: it discloses the auth requirement and, importantly, that a revision is snapshotted automatically before the update (implying reversibility). It still does not clarify whether omitted or null fields are left untouched or cleared, which is the main behavioral ambiguity for a nullable-field update.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two tight sentences, front-loaded with the auth requirement, then the update options, then the side-effect note. No redundancy and nothing that could be cut without losing information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a 4-parameter mutation with no output schema and no annotations, the description covers auth, scope of change, and the automatic snapshot, which is most of what an agent needs. The one residual gap is partial-vs-full replacement semantics, which neither the description nor the schema resolves.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already documents id, data, label, and privacy in detail (including the privacy value mapping). The description's field list maps onto the schema without adding syntax or format information beyond it, so baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ("Update a vault session") and enumerates the three thing that can be changed (payload, label, privacy), so it is trivially distinct from sibling creators like vault-create-session and vault-clone-session. It never explicitly names a sibling alternative, but the verb+resource is unambiguous.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

"[Auth Required]" gives a clear precondition, and the field list implies what the tool is for, but there is no guidance on when to update vs vault-revert-session or vault-clone-session, nor any exclusions. Usage is merely implied rather than stated.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.