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

Annotations already declare readOnlyHint=true and openWorldHint=false, and the description adds genuinely non-obvious behavior: full coverage for Tennessee and Louisiana, and the $50 video diagnostic fallback everywhere else. It does not mention rate limits, response shape, or whether the check is authoritative, but for a simple read-only lookup this is solid added context.

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, zero waste, with the primary purpose front-loaded and the exception/fallback immediately following. Every sentence earns its place.

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?

There is no output schema, so the description must explain outcomes, and it does so for both branches (covered vs. video diagnostic). It could be marginally more explicit about what the covered case returns or implies, but nothing essential for correct invocation is missing.

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 description coverage is 100% ('5-digit US zip code') and there is a single required parameter, so the schema already carries the semantics; baseline 3 applies. The description's mention of 'US zip code' adds no format detail beyond what the schema states.

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 ('check') and resource ('service area' for a US zip code), plus the exact business rule that determines the answer. It is easy to distinguish from siblings like book_repair or diagnose_appliance_problem, which perform different actions.

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?

The description makes the use case clear (verify coverage before in-home repair) and explicitly describes the fallback path for out-of-area zips ('nationwide $50 video diagnostic option'), which routes the agent to an alternative outcome. It never names a sibling tool or states a when-not-to-use condition, so it stops short of a 5.

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