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

Annotations already declare read-only, idempotent, non-destructive behavior, but the description adds meaningful context beyond them: a 15-minute cache, the rust.wiki source, inclusion rules (marketable skins with live Steam price and linked Workshop submission), and an explicit caveat that supply is approximated by Workshop subscriber count. That is a solid disclosure of data provenance and freshness, though it could say more about completeness or rate limits.

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?

It is front-loaded with the core purpose and then structured around field definitions and caveats, so no sentence is genuinely wasted. The second sentence is dense and could be broken up, but overall it is appropriately sized for a data-heavy tool.

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 carries the burden of explaining the return shape and does so clearly, including field meanings, value formula, inclusion criteria, and the approximation caveat. Minor ambiguity remains around whether `top` includes every skin or only a ranked subset, which keeps it from being fully complete.

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?

The tool takes no parameters, so there is nothing to misinterpret; baseline 4 applies. The description instead spends its space documenting output fields, which is appropriate for a zero-parameter call.

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 states a specific resource ('Market cap of the Rust skin market') and concretely lists the return payload (`total_value`, `skin_count`, `by_category`, `top`), so an agent knows exactly what this tool produces. It does not explicitly contrast itself with siblings such as get_market_movers or get_skin_price, so it stops short of a 5.

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 by the data description; nothing says 'use this when you need the whole-market aggregate rather than individual skin prices' or names an alternative. The inclusion criteria and 15-minute cache give useful context but do not constitute when-to-use guidance.

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