One used-phone ad

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

Annotations already cover read-only, idempotent and non-destructive behavior, and the description adds genuinely non-obvious context beyond them: seller name and phone are withheld as personal data, the url is where those appear to signed-in visitors, and market_price_toman is the site's own estimate rather than an observed price. That is real disclosure of data quirks an agent could otherwise misread.

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?

The field enumeration is front-loaded and earns its place because there is no output schema; the two trailing caveat sentences are short and purposeful. Slightly list-like phrasing but no wasted prose.

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?

With one required parameter, no output schema, and full annotation coverage, the description does what it must: it previews the return fields and flags the two data caveats (missing contact info, estimated market price). Only the lack of guidance on follow-up tools or error behavior keeps it from the top score.

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% and the single parameter is documented as an ad_id sourced from mi_used_search, which is the key semantic link an agent needs. The description adds nothing further on the parameter, so it sits at the baseline-plus level rather than above 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?

The description opens with a specific verb and resource ("Read one used/new phone ad on Mobile.ir") and enumerates the returned fields, so an agent knows exactly what it gets. It does not explicitly name the sibling it complements (mi_used_search), but the singular "one ad" framing makes the search-vs-fetch distinction fairly clear.

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 only implied: this is the detail lookup that follows a listing search, reinforced by the schema note that ad_id comes from mi_used_search. There is no explicit "use this when..." statement or exclusion of alternatives such as mi_used_search or mi_phone.

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