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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open-world), so the bar is lower. The description adds genuinely non-structured context: a per-call price ($0.01 USDC via x402 on Solana), the batch cap of 100 CVEs, and the fact that historical dates are supported. It does not cover error behaviour for invalid or unknown CVE ids, keeping it from a 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?

One dense paragraph, front-loaded with what the tool returns before sibling routing, pricing and the HTTPS mirror. Every sentence carries information, though the payment and endpoint details could be split for faster scanning.

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?

No output schema exists, so the description compensates by naming the returned fields (probability, percentile rank, band) and the model-run semantics. Combined with annotations and a fully documented two-parameter schema, an agent has everything needed to call it and interpret the result.

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 100%, so production and error semantics for both parameters are already documented in the schema. The description restates the 100-CVE cap and the latest-vs-historical date choice but adds no syntax or format detail beyond the schema, so the 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 resource (FIRST EPSS exploit-prediction scores), a concrete scope (up to 100 CVEs) and what the values mean (probability of exploitation in next 30 days, percentile rank, band). It names the sibling tools it complements (cve_lookup, cisa_kev), so an agent can place it against alternatives immediately.

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 context — 'Complements /v1/cve-lookup and /v1/cisa-kev for vulnerability prioritisation' — which tells the agent when this tool fits into a workflow. It does not state exclusions or say what to use instead when a single-CVE lookup is all that's needed, so it stops short of full when/when-not guidance.

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