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

Annotations already carry readOnlyHint and idempotentHint, so the 'READ ONLY' prefix is largely redundant, but the description adds real behavioral context: it returns the likely next step plus a linked guide, and it explicitly declines legal-effectiveness judgments. That limitation is valuable and unavailable from 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?

Front-loads the safety marker, then purpose, then sibling routing, then the scope limitation. The long status enumerations are purposeful but sit in the middle rather than delaying the key routing information.

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?

An output schema exists, so return-format explanation is unnecessary, and the description covers scope, ambiguity routing, and the legal-effect caveat. Minor gap: it doesn't say what happens with an unrecognized status string.

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?

Only one parameter, and the schema already documents it at 100% coverage including an example value. The description's status examples add flavor but no syntax beyond the schema, so the baseline 3 is appropriate.

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 (explains) plus the two distinct resource vocabularies it decodes (USPS tracking statuses and Piloxa transaction states) with concrete examples in quotes. An agent can immediately tell this apart from get_certified_letter_status.

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?

Explicitly routes the agent: use this one for a general status explanation, use get_certified_letter_status for a specific letter prepared in this conversation. That is a direct when/when-not with the alternative named.

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