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

With no annotations the description must carry the full behavioral burden, and it does well: it declares the 15-minute staleness (twice), that access is free via x402, that the response includes per-venue detail, cross-venue divergence and the last 1h move, and that resolved markets return '410 RESOLVED' with the outcome. It omits rate limits and any auth detail beyond pricing, keeping it just short of 5.

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?

Front-loaded with the core capability, then progressively adds output shape, error behavior, slug lookup, and the delayed-vs-realtime contrast. Slightly redundant, restating the 15-minute delay, and the HTTP/docs bracket adds noise, but every other clause earns its place.

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 and no annotations, the description compensates well by describing the return shape (per-venue detail, divergence, last 1h move), the resolution case, and the identical shape to the realtime sibling. Only the venue enum semantics and rate/access limits are left uncovered.

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 coverage is 0%, so the description must compensate. It adds meaningful context for slug ('canonical market slug', discoverable via search) but does nothing to explain the venue enum values (kalshi/polymarket/blend) or the 'blend' default, which the schema also leaves undocumented. Partial compensation only, so baseline 3.

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+resource (blended event probability across Kalshi and Polymarket for a canonical market slug) and names the exact differentiating scope: the 15m-delayed, free variant. It is clearly distinguishable from the sibling probability_get (realtime) without opening either 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?

Explicitly routes the agent: 'Use the paid endpoint for realtime data' names both the alternative and the condition that selects it, and 'Find slugs via /v1/probability/search' tells the agent how to obtain the required slug. Nothing is left to inference.

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