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

Annotations already declare readOnly/idempotent/non-destructive, but the description adds behavior the annotations cannot: the response is cached, and the call is gated behind an Indie or Agency plan (a trial counts). It also explains that a usage allowance with used/limit/remaining/resets_at is returned, which tells the agent to watch for quota exhaustion.

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 sentences, front-loaded with the routing purpose before the payload detail and the plan caveat. Every clause carries information: what it returns, what to do when data is missing, and what the call costs.

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?

No output schema exists, so burden falls on the description to describe returns, and it does so field-by-field along with the plan and quota prerequisites. Nothing an agent needs in order to call this zero-arg tool or interpret its result is missing.

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?

Zero parameters, so the schema baseline is 4 and there is nothing parameter-level to explain. The description does add value by naming the response fields (meta_pages, tiktok_accounts, allowance counters) an agent should look for, even though these are outputs rather than inputs.

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 resource (every competitor the account tracks) and enumerates exactly what comes back: linked meta_pages, tiktok_accounts, last page scan, and today's lookup allowance. The opening 'Start here for competitor ads' positions it against the many sibling ad_spy tools without ambiguity.

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?

Explicit entry point ('Start here'), plus a concrete routing rule for the edge case: a competitor with no linked page needs sonar_ad_spy_scan then sonar_ad_spy_link. Names the alternative tools and the condition that selects them, so the agent never has to guess a next step.

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