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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description earns credit beyond that by naming the upstream source (Polymarket Gamma API) and disclosing a per-call cost of $0.003 USDC via x402, a metering detail an agent cannot get from any structured field.

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?

The core purpose is front-loaded in the first clause, followed by the return-field inventory, source, and price. The long field list is dense but each entry helps the agent judge whether the payload answers its question; only minor trimming would improve it.

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 full burden of describing return values, and it does so with a concrete field inventory (prices, Yes probability, bid/ask, volumes, status, URL). Combined with the disclosed source and cost, an agent has everything needed to decide and call correctly.

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% and the single id parameter is fully documented with an example, so the schema does the heavy lifting. The description's "numeric id or slug" restates rather than extends that meaning, making the high-coverage baseline of 3 the right 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?

"One Polymarket market by numeric id or slug" states a single-resource fetch with an explicit key type, which cleanly separates it from the plural sibling polymarket_markets (list/search). It then enumerates the payload contents, so an agent knows both what it does and what it returns without opening the schema.

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 phrase "by numeric id or slug" implicitly tells the agent this requires a known identifier, so it is the wrong tool for discovery. However, it never states when-not to use it or names polymarket_markets as the alternative for listing or searching, leaving that inference to the agent.

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