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

Annotations already declare destructiveHint=true and idempotentHint=true, so the bar is lower. The description adds genuine value beyond them: required sign-in plus Aisle membership, and an explicit list of immutable attributes, which tells the agent the blast radius of the write. It does not explain the destructive/clearing semantics (empty string wipes a field), though the schema covers that.

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?

Three sentences, front-loaded with what can be updated, then constraints, then requirements. Minor redundancy: 'The guest identifier is required' restates the schema's required list and could be dropped without loss.

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 10-parameter mutation with no output schema, the description covers scope, eligibility, exclusions, and auth, which is most of what an agent needs. It could say a bit more about partial-update behavior (only supplied fields change) and the empty-string clearing convention, but nothing critical is missing.

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 every parameter is already documented with enums and clear semantics (including the empty-string clearing behavior). The description merely echoes the updateable field groups, adding no syntax or format detail beyond the schema, so the 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 (Updates) with a clear resource (guest) and enumerates the mutable field groups, which cleanly separates it from add_my_guest and remove_my_guest. The eligibility constraint ('guest already recorded as 13 or older in the selected wedding') further sharpens its identity.

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?

Gives clear when-to-use context (guest must be 13+ in the selected wedding) and explicit exclusions (cannot change age bands, guest notes or dietary details), plus an auth precondition. It stops short of naming which sibling to use instead when those exclusions apply (e.g. for dietary details), so it is not a full 5.

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