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

Beyond the readOnly/idempotent/openWorld annotations, the description discloses concrete behavioral facts the annotations cannot: the default result ordering (volume), the quota and pricing model including the x402 endpoint, and the shape of the returned data. Rate limits and per-call cost are exactly the kind of context an agent needs before calling.

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 tight sentences: the capability and return fields are front-loaded, then the quota/pricing line. Every clause carries information — no filler, no restatement of the title.

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 compensates by listing the returned fields (event, market, outcome prices, volume, liquidity, end date, link) and the sort order. Combined with full schema coverage on the three parameters, an agent has everything needed to call and interpret this tool.

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 the baseline is 3; the description adds modest value by clarifying that prices are implied probabilities on a 0-1 scale and that results are volume-ranked, which helps interpret the output. It still does not explain how 'all' source merging behaves or how query matching works, so it stays just above baseline.

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 opens with a specific verb and resource ('Search open prediction markets on Polymarket and Kalshi') and enumerates the fields returned, so the agent knows exactly what comes back. No sibling tool covers this ground, and the description makes that distinct scope self-evident.

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?

It gives clear operational context for invocation: a single call covers both venues, results are sorted by volume, and there is a free tier of 25 calls/day per IP with a paid x402 fallback at $0.005/call. It stops short of naming exclusions or pointing to an alternative tool for adjacent needs such as historical or closed markets.

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