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

Annotations already flag a non-readonly, open-world, non-idempotent call, and the description corroborates with "WRITE tool". It adds genuinely useful context the annotations cannot carry: it spends one of the account's daily Ad Spy lookups, same-day re-opens are free, over-allowance calls return a cached copy flagged with meta.stale and a meta.note to relay, and an Indie/Agency plan plus write-scoped auth is required.

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?

Three dense sentences, each carrying distinct information (purpose, routing, cost/auth), with the tool's own verb and resource front-loaded. The quota and plan constraints are packed into one long clause, which is slightly heavy but not padded.

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, and the description compensates by naming the relevant response fields (allowance, meta.stale, meta.note) and the auth/plan prerequisites. For a single-parameter search tool, nothing needed to call it correctly 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?

Only one parameter and the schema already documents it at 100% coverage with an example ("Brand or company name, e.g. \"duolingo\""). The description's "free-text search ... by brand or company name" restates the schema rather than adding syntax, normalization, or matching-behavior detail, so the high-coverage baseline of 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 ("free-text search for Facebook advertiser pages") plus the qualifying scope "by brand or company name, not tied to a tracked competitor", which separates it from competitor-bound siblings like sonar_ad_spy_scan or sonar_ad_spy_competitors.

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?

Names the two concrete follow-up paths and their conditions: open a result with sonar_ad_spy_open_page, or attach it to a competitor with sonar_ad_spy_link. It also states the quota consequence of calling, which is the main decision factor versus other discovery tools.

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