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

Beyond the readOnly/idempotent annotations, it discloses the selection rule (cheapest priceable plan per vendor), the null case for quote-only or unpriceable-at-volume vendors with an explicit no-fabrication guarantee, and the defaulting plus echoing of avgCallMinutes for reproducibility. These are exactly the behavioral traits an agent cannot infer from structured fields.

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?

The key output semantics are front-loaded in the first sentence and each subsequent sentence adds a distinct fact (non-telephony behavior, null policy, defaults). It is dense but free of filler; the trailing default note could have been folded in more tightly.

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 must carry the return semantics, and it largely does: per-vendor normalized cost, cheapest-plan selection, null handling, and assumption echoing. The remaining shortfall is the unexplained mechanics of callsPerMonth, which matters for a pricing-calculation tool.

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 only 33%: section is well documented but callsPerMonth and avgCallMinutes carry no schema description. The description compensates for avgCallMinutes (default 3, echoed in assumptions) and implies callsPerMonth is the volume at which per-call/per-minute pricing is annualized, but it never spells out how that volume drives the calculation, leaving a real gap.

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 opening sentence names a specific computation (effective monthly cost per vendor at a chosen call volume) and defines the normalization operation across flat, per-minute and per-call billing. This distinguishes it from siblings like compare, find_best, and get_benchmark, which do not return a normalized per-vendor figure.

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 clarifies one usage branch — non-telephony catalog themes return base monthly price — and states that only the cheapest priceable plan per vendor is returned. However, it never says when to reach for this tool instead of compare, find_best, or get_cost_decoder, so routing is left implicit.

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