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

Annotations already declare readOnly, idempotent, non-destructive, closed-world access, so safety is covered. The description adds genuinely new context: every returned field carries its source page and read date, and the optional calls parameter triggers a computed monthly cost — provenance and derived-value behavior the annotations cannot express.

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?

Two sentences and a source URL, with the field inventory and the input-format hint front-loaded. The first sentence is a long run-on list, but every clause names an actual returned attribute, so no sentence 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?

With no output schema, the description carries the return-value burden and does so by enumerating the returned facts plus their provenance. It stops just short of 5 by leaving cross-tool routing (versus compare_vendors/get_rankings) and unknown-vendor behavior unaddressed.

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 baseline is 3, but the description earns extra credit by clarifying that `vendor` accepts either an id or a name and giving concrete examples ("NextPhone", "Smith.ai", "Rosie"), plus confirming the calls parameter can be any volume, not just 100/200.

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 concrete resource — a single vendor's ranking facts — and enumerates exactly which facts (plans, cost at 100/200 calls, billing model, contract terms, trial, spam billing, integrations, score). The singular scope implicitly distinguishes it from compare_vendors, but no sibling is named explicitly.

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: fetch this when you need details on one vendor. There is no explicit statement about when to prefer compare_vendors or get_rankings instead, and no prerequisites or failure behavior (e.g. what happens for an unknown vendor).

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