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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so the safety profile is covered. The description adds valuable behavioral context: the paid nature ($0.02/call), the sampling rate (~1/min), the normalized series, the 404 for untracked markets, and the exact payment handshake. It doesn't contradict annotations. It could mention rate limits or data retention, but the payment and 404 behavior are well disclosed.

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 description is dense but every sentence earns its place: payment cost, data shape, sampling, the two-step payment flow, and the 404 behavior. It is front-loaded with the most critical fact (paid) and the resource scope. No fluff or repetition 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?

For a tool with no output schema, the description explains the return format ([ts, yesUsd, noUsd]) and the payment handshake, which is the main complexity. It doesn't specify pagination or time range details beyond '24h', but the sampling and series normalization are covered. The payment flow is fully described, making it complete enough for an agent to 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%, so the schema already documents both parameters. The description adds meaning by explaining that marketId comes from predict_markets (a sibling tool) and that x402_payment is the base64 X-PAYMENT payload from the first call. This goes beyond the schema's bare descriptions, though it doesn't detail the format of the payment requirements array.

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 states a specific verb ('predict_history' implies retrieving history), a clear resource ('24h odds history for one tracked Polymarket market'), and the exact data shape ('[ts, yesUsd, noUsd] points sampled ~1/min'). It distinguishes itself from siblings by specifying it is for a single tracked market and mentions the payment model, which is unique among the listed tools.

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 description explicitly explains the two-step usage: first call without x402_payment to get payment requirements, then pay and call again with x402_payment. It also states the condition for an untracked market (uncharged 404) and clarifies that charges only occur when a result is returned. This is clear when-to-use guidance, though it doesn't name alternative tools for similar data, but the payment flow is the key usage context.

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