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

Annotations already declare destructiveHint=true, idempotentHint=false and readOnlyHint=false, so the safety profile is covered. The description adds real behavioral context beyond that: only passed fields change, and custom_attributes are merged rather than replaced. It stops short of explaining what makes this destructive or whether the merge applies to additional_attributes too.

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 with the mutation semantics front-loaded and the merge caveat second; every clause carries information and nothing is repeated from the schema or annotations.

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 7-parameter mutation with no output schema and low schema coverage, the description covers the core partial-update contract but omits the custom_attributes vs additional_attributes distinction, validation behavior (e.g. maxLength failures) and what a successful update returns. Adequate but with clear gaps.

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 only 14% (just phone_number's E.164 note), so the description should compensate more than it does. It names name/email/phone/identifier but leaves the two object parameters ambiguous, never distinguishing custom_attributes (merge) from additional_attributes (unexplained), which is the highest-value ambiguity for this 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 (Change) plus the resource (a contact) and enumerates the mutable fields, so the agent immediately knows this is a partial-update tool rather than a create/delete. It does not explicitly name siblings like create_contact, delete_contact or get_contact, so differentiation is inferred rather than stated.

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?

There is no explicit when-to-use guidance, no prerequisites (e.g. that contact_id must already exist), and no routing to alternatives such as create_contact or search_contacts. The tool's role as a mutation is only implied by the verb 'Change'.

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