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

Annotations already declare readOnly/idempotent/non-destructive/openWorld, so the safety profile is covered. The description adds value with "Stores nothing and costs nothing", which reassures the agent there are no side effects or billing consequences, plus a preview of the return contents. It does not cover auth or rate-limit behavior, so not 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?

Two tight sentences with zero filler, and the actionable sequencing instruction is front and center. Every clause earns its place by either stating the outcome or the return payload.

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 usefully enumerates what is returned (price, trial terms, how the service works), and it is complete for a single-parameter, side-effect-free check. An agent has everything needed to call it correctly 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% and the single postal_code parameter is fully documented in the schema, including format and Canadian-only scope. The description adds no parameter-level meaning beyond that, 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 (checks) and resource (a building) and goes further to enumerate what the caller gets back: a buzzer number decision, price, free-trial terms, and how the service works. This is well beyond the title and clearly separable from the partner_* and *_phone_code siblings.

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?

"Call this first" gives explicit ordering guidance, which is exactly the kind of routing an agent needs in a multi-step onboarding flow. It does not name a specific alternative or state when-not to use it, so it stops short of a 5, but the sequencing instruction is unambiguous.

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