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

Annotations already declare readOnlyHint=false, destructiveHint=false, openWorldHint=false, so safety profile is covered; the description adds real value beyond them by disclosing the required `topics:write` scope and the domain behavior that STOP remains a global opt-out overriding topic subscriptions. It stops short of noting that creation is not idempotent (annotations say idempotentHint=false), which leaves duplicate-name behavior unaddressed.

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 purpose front-loaded, followed by a compact scope line. Every sentence earns its place, though the trailing 'Scope:' line is slightly detached boilerplate rather than integrated into the main statement.

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?

Output schema exists so return values need not be described, annotations cover the safety/mutation profile, and the parameter shape is fully documented in the schema. The description adds the two things structured fields can't supply: the required write scope and the STOP-override semantics, which is enough to call the tool correctly.

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% and the nested body already documents `{ name }` plus optional `description` and `default_opt_in`, so the schema carries parameter meaning. The description adds nothing further about field semantics (e.g., name uniqueness or what default_opt_in defaults to), 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 and resource: 'Create an SMS subscription topic' — an agent immediately knows this is the creation operation for the SMS topics family (list/get/update/delete siblings are distinguishable by name). It does not explicitly reference those siblings, but the verb+resource pairing 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?

Usage is implied by the verb (use this to create a topic), and the 'STOP still opts a number out of every SMS' note gives useful context on when the topic-level opt-out matters. However, it never states prerequisites (e.g., an SMS brand/number must exist first) or routes the agent to alternatives such as sms_topics_update when a topic already exists.

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