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

Beyond readOnlyHint/openWorldHint, the description discloses the auth model ("the letter_id is the credential"), the redaction behavior that depends on whether the caller holds the originating API key, and the conditional nature of proof links by postage type. These are non-obvious behavioral traits an agent could not infer from annotations or schema.

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?

Three sentences, front-loaded with what is returned before the operational caveats. The status enumeration and postage-type parentheticals are dense but each earns its place by removing ambiguity about return values.

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 takes on the burden and does so thoroughly: it names the return payload (status, timeline, proof links) and the redaction rule. For a single-parameter read tool, nothing an agent needs in order to call it correctly 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 coverage is 0%, so the description must carry the parameter meaning: it explains that letter_id is not just an identifier but the credential granting access, which is meaningful guidance beyond the regex pattern. It does not describe the format or how to obtain the id, keeping it just short of a 5.

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 description states a specific verb and resource ("Returns the current status of a letter") and enumerates exactly what comes back: status values, timeline, and proof links. The sibling tools (quote_letter, send_letter, get_coverage) are clearly distinct activities, and this reads as a pure read/lookup operation, so an agent can route to it unambiguously.

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?

Implicit context is clear: use this to follow a letter after it has been sent, and no alternative tool competes for that job. It also states a useful precondition ("No account is needed"), but it never explicitly says when not to use it or names a sibling as the alternative for a related need.

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