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

Annotations include readOnlyHint=true, so the read-only nature is already known. The description adds valuable behavioral context: the distinction between 'not listed' and flat/zero, and the rarity of coverage. This goes beyond the annotation and clarifies interpretation of results.

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 sentences, each earning its place: the first states the core function, the second provides coverage context, and the third clarifies an important interpretation caveat. No redundancy or filler.

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 simple, one-parameter read operation with no output schema, the description covers the essential elements: what data is returned, the limited universe, and the non-zero meaning of 'not listed.' It could mention the exact output fields (e.g., funding rate value, open interest amount) but is otherwise 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 schema provides 100% coverage for 'ticker' with a basic example. The description enriches this by clarifying that only a small subset of tickers is valid for this venue, which is essential for interpreting 'not listed' responses. This adds meaning beyond the schema's simple type description.

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 clearly specifies the resource: funding and open interest for a single ticker on the perpetual venue. It distinguishes from list_equity_perp by emphasizing 'single name,' though it lacks an explicit verb like 'retrieves' or 'returns.'

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?

Provides strong contextual guidance by warning that most tickers are not listed (51 of ~5,400) and that a 'not listed' answer means no coverage, not zero positioning. This helps set expectations, though it does not explicitly name alternative tools or when to prefer them.

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