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

Annotations already declare destructiveHint=true, so the safety profile is partly covered; the description's 'This MODIFIES live store data' reinforces rather than extends that. It does add the PATCH/partial-update behavior (unmentioned fields are left unchanged), but omits reversibility, permission requirements, and error behavior on a bad id.

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?

Four short, front-loaded sentences with the mutation warning placed prominently. Minor redundancy between the description and the destructiveHint annotation, but no filler that obscures the key facts.

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 destructive mutation with no output schema, the description covers purpose, partial-update behavior, and the live-data impact. Remaining gaps (auth, id-not-found handling, whether the updated record is returned) are moderate but not central to correct invocation.

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 real semantic value beyond the schema by clarifying that only supplied fields are changed (PATCH semantics). The re-listing of first_name/last_name/email is partly redundant with the schema, keeping this from a 5.

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), a specific resource (customer profile fields), and enumerates the mutable fields. It is clearly distinguishable from the read sibling foxy_get_customer and from foxy_update_subscription, and it names the backing endpoint (PATCH /customers/{id}).

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 line 'Provide only the fields you want to change' gives clear context for partial updates, which is genuinely useful guidance. However, it never states when to use this tool versus alternatives (e.g., foxy_update_subscription) or any preconditions such as needing an existing customer id from foxy_get_customer.

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