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

Annotations already declare idempotentHint=true, destructiveHint=true, and readOnlyHint=false, so the safety profile is covered. The description adds the meaningful merge semantics (only present fields are mutated), which is not derivable from annotations, but it omits permissions, validation failures, and what happens to omitted nested objects.

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?

It is short and front-loads the operation before the partial-update rule. The middle fragment 'Writable fields of a site template' is a dangling noun phrase that reads like a leftover header and earns little, keeping it out of 5 territory.

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 13-parameter tool with nested objects and no output schema, the description is thin, but 100% schema coverage and the annotations carry most of the burden, and the PATCH rule fills the main behavioral gap. It is adequate but not complete.

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 one of the 13 parameters (including deeply nested limits, actions, schedule, and location_targeting fields) is already documented in the schema. The description adds no syntax, format, or constraint detail beyond that, 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?

The first sentence states a specific verb+resource ('Update a site template') that cleanly maps onto the tool name and distinguishes it from the sibling create/delete/get/list site-template tools by naming the mutation. It does not explicitly route against update_site or create_site_template, but the 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?

The phrase 'For PATCH, provide at least one; only the fields present are changed' tells the agent it is a partial update and that at least one field is needed, which is genuine usage guidance. However, there is no explicit when-to-use versus create_site_template / delete_site_template / update_site, so the guidance is implied rather than comparative.

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