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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so safety is covered. The description adds genuinely new behavioral content: it is a coverage/limits document that explicitly includes what is *not* modelled and cites official sources, which tells the agent to expect caveats and provenance rather than calculations. The 2026 vintage is also useful context that annotations cannot carry.

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 sentence, front-loaded with the resource and scope, followed by the call-to-action. No filler. The phrasing 'The United States rules the calculators apply' is slightly compressed and takes a second read, which is the only thing keeping it from a 5.

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 parameters and no output schema, the description must carry the return-content burden, and it does: rules, options, non-modelled areas, and sources. An agent knows what it will get and why it matters. A brief note on the format of the response (e.g. a static reference text) would close the last gap.

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?

There are zero parameters, so the baseline of 4 applies; there is nothing for the description to disambiguate. It correctly avoids inventing parameter discussion for a no-arg tool.

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 names the resource precisely: the US rules the calculators apply for 2026, the options they accept, what is not modelled, and the official sources. That is clearly distinct from the siblings (net_salary, employer_cost, compare_with_netherlands), which compute rather than document. It stops short of a crisp leading verb ('returns'/'describes'), so the phrasing reads as a noun phrase rather than an action.

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 an explicit trigger: call it before answering a question the other tools may not cover. That is real routing guidance rather than implied usage, and it frames this as a pre-flight reference lookup. It does not state a when-not case or name a specific sibling as the alternative path, which keeps it below a 5.

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