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

Goes well beyond the readOnly/idempotent annotations: discloses that no spend or impression data exists outside the EU, that longevity and variant counts are the substitute signals, that media URLs are expiring CDN links and library_url is the permanent one, and what refresh_due=true implies. The compact/full payload tradeoff and plan gating are exactly the kind of context annotations cannot carry.

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?

Front-loads what is returned, then moves to signals, payload shape, freshness, and access requirements in a logical order. The compact-vs-full point is stated twice (parenthetical plus the media URL sentence), which is minor redundancy in an otherwise dense, purposeful block.

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 9-parameter read tool with no output schema, the description fully describes the return surface (stats block, filtered ads, daily history) and flags the key constraints (EU-only reach data, expiring media, plan requirement). Nothing an agent needs in order to call it and interpret the result is left implicit.

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 100%, so the baseline is 3; the description still earns credit by explaining why min_days matters (longevity is the honest winner signal, 30/60/90) and the size/expiry tradeoff between compact and full. It adds interpretive value on top of an already well-documented schema rather than restating it.

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 — a Facebook page's cached Meta ads — and enumerates the payload (ad stats, filtered ads with copy/CTA/landing URL/placements/days running/longevity tier, daily active-new history). It names related siblings (sonar_ad_spy_refresh, sonar_ad_spy_competitors, sonar_ad_spy_open_page) by role, so an agent can place it in the family without opening other schemas.

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?

Explains the acquisition path (cached read; refresh via sonar_ad_spy_refresh when refresh_due is true) and states the plan prerequisite (Indie or Agency, trial counts). It does not explicitly contrast itself with sonar_ad_spy_ad_analysis or sonar_ad_spy_analyze_ad, which are the closest siblings, so the when-not guidance is incomplete rather than explicit.

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