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

Annotations already cover the safety profile (readOnly, non-destructive, open-world), so the bar is lower. The description adds genuinely non-obvious behavior: the tool renders its own card and the agent must not restate the details in prose. It does not cover failure modes for an unknown avatar_id, which keeps it from a 5.

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?

Two sentences, zero waste, with the resource and returned fields front-loaded and the rendering directive placed after. Every sentence carries actionable information.

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 no output schema, the description correctly compensates by naming the fields returned (preview, seller, size, free/paid). Combined with annotations covering safety, an agent has enough to call it correctly; only error behavior for an invalid id is unaddressed.

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?

There is a single parameter with 100% schema coverage, including a pattern and the 'Marketplace listing id' description, so the schema does the heavy lifting. The description adds only the framing that the id refers to one Ania avatar, which is marginal beyond the schema.

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 uses a specific verb and resource ('Get the details of one Ania avatar') and enumerates the returned fields: preview, seller, size, and free-vs-paid listing status. It does not name or contrast with siblings such as my_avatars or show_avatar, so the agent must infer that this is the single-item lookup.

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: 'one Ania avatar' signals a single-item fetch versus list tools, and the second sentence tells the agent how to present the result. There is no explicit when-to-use/when-not or named alternative, so selection guidance is left to inference.

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