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

Annotations cover safety (readOnly, openWorld), but the description adds the non-obvious operational facts: it is read-only metadata with no traders or wallet data, costs $0.01 USDC per successful call on Base, and requires an x402-capable wallet client. Cost and payment-client requirements are exactly the kind of behavior an agent cannot infer from structured fields.

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 tight sentences, front-loaded with what is read and how much, followed by data exclusions and then payment/auth constraints. Every sentence earns its place with no redundancy.

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 two-parameter, no-required-input tool with no output schema, the description covers the data returned, the scoping modes, the privacy boundary, the price, and the client prerequisite. Nothing needed to call it correctly is missing.

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 description coverage is 100%, so slug and maxItems are already documented with their formats and defaults. The description restates the slug/active-market split and the 20-item ceiling but adds no syntax or format detail beyond the schema, so baseline 3 applies.

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 ('Read ... Polymarket markets') with precise scope: up to 20 active public markets or one exact slug. It also names the returned fields (outcome prices, implied probabilities), so an agent knows exactly what this tool yields and can distinguish it from every sibling in the list.

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?

The two usage modes are explicit: omit the slug for active markets, supply an exact slug for a single market, and the schema reinforces the 24-hour-volume ranking. No competing sibling exists to route against and no when-not guidance is given, which is the only gap.

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