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

With no annotations, the description carries the whole burden. It usefully discloses cost tier ('FREE') and the exact data composition (11 sectors, four return windows), but says nothing about data freshness/delay, update cadence, or failure behavior if the market is closed. For a zero-parameter read-only snapshot, that is adequate but not rich.

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 short sentences, front-loaded with the core payload and finished with the use case. 'FREE.' is a single-token qualifier that earns its place given no annotations exist to declare cost or safety. Nothing is redundant.

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 an output schema present, return structure needn't be explained, and with zero params and no annotations the surface area is small. The description covers what is fetched, at what grain, and why. A note on data delay or market-hours behavior is the only meaningful gap.

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 no parameter semantics to explain; baseline 4 applies. The description's mention of return windows correctly signals what the single fixed call returns rather than implying any configurable inputs.

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 ('Get market sector performance') and then spells out the exact payload: the 11 GICS sectors via SPDR ETFs ranked by today's move with 5-day, 1-month, and YTD returns. That level of specificity makes it unmistakable against siblings like quote, price_history, or options_chain, which operate on single instruments rather than cross-sector aggregates.

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?

'For rotation, breadth, and macro positioning at a glance' gives a clear, concrete use case that tells an agent when this tool is the right reach. It stops short of naming an alternative or stating exclusions (e.g., use quote for a single ticker), so it is clear context rather than full routing guidance.

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