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

Annotations only supply destructiveHint=true; the description adds genuine behavioral context beyond that by disclosing PATCH partial-update semantics ('only included fields change'), which tells the agent omitted fields are preserved. It stops short of stating permission requirements or whether changes are reversible, so it is not a full 5.

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 tightly packed segments with the mutation warning front-loaded, then the endpoint, then the passthrough rule. Every clause earns its place and there is no filler.

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 mutation tool with no output schema and minimal annotations, the description covers the key gaps: mutation intent, endpoint, and partial-update semantics, plus handling of the nested `fields` object. It omits auth/permission expectations and error behavior, which is the only meaningful shortfall.

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 coverage is 100%, so the baseline is 3, but the description adds meaning the schema does not: it names the array fields (email_addresses/phones/addresses) that must go through the `fields` passthrough and explains the merge behavior with the typed fields. This is real added value over the structured schema.

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+resource ('updates an existing guest') and pins it to the concrete API operation (PATCH /v2/guests/{id}). This cleanly separates it from the sibling create_guest, get_guest, and list_guests tools without the agent needing to open a schema.

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?

The description implies usage (it is the update path for an existing guest) but gives no explicit when-to-use vs when-not, and no alternative routing when a create or read is actually wanted. The one real directive — route arrays through `fields` — is useful but is parameter guidance rather than tool-selection guidance.

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