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

Annotations already declare destructiveHint=true, idempotentHint=true, and readOnlyHint=false, so the safety profile is documented. The description adds the dual-mode framing (subscribe vs. unsubscribe via the same call), which clarifies what a false value does, but it does not warn that unsubscribing removes a contact from a communication stream or mention idempotency/rate behavior.

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?

A single sentence, front-loaded with the action, plus a short parenthetical that illustrates the use case without padding. Efficient, though the example could be mistaken for schema-level detail.

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 mutation tool with no output schema and full annotation coverage, the main things an agent needs — what the call does in both directions and where topic IDs come from — are present. Missing detail about interaction with consent/opt-out state or error conditions when the contact/topic does not exist keeps it from a 5.

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 75% and the undocumented parameter is exactly the required boolean `subscribed`; the description's 'subscribe ... or unsubscribe' supplies its meaning, which the schema does not. The example topics and the subscribe/unsubscribe framing add real value over the schema, though the `source` parameter goes unmentioned.

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 (subscribe/unsubscribe) on a specific resource (a contact's topic), which distinguishes it from list-level tools like add_to_list and read tools like get_contact_topics. It does not explicitly name a sibling for disambiguation, so it stops short of a 5.

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 by showing the subscribe/unsubscribe pair and giving example topics, but never says when to use this instead of set_consent, add_to_list, or get_contact_topics. The schema's 'see list_topics' hint covers topic lookup, but that guidance lives in the schema, not the description.

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