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

Annotations already declare readOnly and non-destructive behavior. The description adds valuable context: it includes intro-price traps, per-user vs flat pricing, and price provenance with a date. It does not specify freshness/update policy, but the added context goes beyond the annotations.

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 dense sentences front-load the core purpose and scope, then add caveats and provenance. No wasted words; examples improve clarity without bloating the text.

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?

For an informational tool with 2 optional parameters and no required inputs, the description is nearly complete: it states the ranking basis, included pricing nuances, and data provenance. It does not describe the exact output format, but 'ranked by two-year cost' implies the returned structure sufficiently.

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. The description adds meaning by mapping provider categories to the `need` enum (forward, mailbox, suite, private) and clarifying that cost depends on mailbox count via per-user vs flat pricing.

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?

Description clearly states it ranks custom-domain email providers by two-year cost, naming concrete provider categories (free forwarding, cheap mailboxes, office suites, encrypted). This strongly differentiates it from sibling tools like compare_tld_prices, which focus on domain pricing rather than email hosting.

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 scope is clear: use this when comparing email hosting providers for a custom domain. It does not explicitly name alternative tools or conditions for when not to use it, so it stops short of a 5, but the context is unambiguous.

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