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

Annotations already declare a safe read (readOnlyHint true, destructiveHint false, openWorldHint false), so the safety profile is covered. The description adds auth prerequisites ('needs the inbox id and secret') and a cost signal ('Free'), which are genuine additions beyond structured data. It does not mention pagination/limit behavior, keeping it short of 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 compact clauses, front-loaded with the operation and its result fields, followed by cost and auth notes. No filler, though the second clause is terse enough to be slightly telegrammatic.

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 a read-only 4-parameter listing tool with no output schema, the description covers what is returned (sender, subject, size), the paging anchor, cost, and auth. Minor gaps remain around limit/pagination behavior, but nothing critical is missing for correct invocation.

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 75% and the schema documents after, secret, and inbox_id; only limit lacks a schema description. The description restates the 'after a sequence number' semantics but adds nothing about limit or default/max bounds, so it is baseline-level when the schema does most of the work.

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?

Specific verb (list) plus resource (messages of an inbox) and it names the returned fields (sender, subject, size) and the paging anchor (after a sequence number). It is not explicitly differentiated from read_message or wait_for_message, but the resource and shape are clear enough to separate it from create_inbox/delete_inbox.

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 phrase 'after a sequence number' implies incremental polling, and the mention that it 'needs the inbox id and secret' gives a prerequisite, but there is no explicit when-to-use vs read_message, wait_for_message, or get_otp. Usage is implied rather than stated.

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