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

Annotations already declare readOnly, idempotent, and closed-world, so the safety profile is covered. The description adds real behavioral context beyond that: the fixed one-month window, daily granularity, and the upstream source (FIRST). It omits what happens for CVEs with no EPSS data and does not mention pagination or result size, which for a daily series would be useful.

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?

A single tight sentence with zero filler, front-loading the resource and the time scope before the parenthetical definition. It reads as a fragment rather than a sentence, and 'last month' is slightly ambiguous relative to a caller's current date, but no wording is wasted.

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 one-parameter, read-only lookup with no output schema, the description tells the agent what the response represents (daily EPSS probability over the previous month) and where it comes from. Missing only edge-case behavior for CVEs lacking EPSS history and confirmation that the window is fixed rather than caller-controlled.

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?

With a single parameter at 100% schema description coverage, including a regex pattern and an example, the schema fully carries parameter semantics. The description adds nothing about the id beyond what the schema states, 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 verb+resource: retrieves a CVE's EPSS score history, day by day, over the last month, and even defines EPSS inline. It does not, however, distinguish itself from the nearest sibling get_epss_movers, leaving the agent to infer which one gives a per-CVE trend versus an aggregate ranking.

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?

Usage is only implied: an agent can infer this is for inspecting one CVE's exploitation-probability trend over time. There is no explicit when-to-use framing, no mention of prerequisites (e.g. whether EPSS data exists for older CVEs), and no naming of get_epss_movers or get_timeline as alternatives.

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