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

Beyond the read-only/idempotent annotations, it discloses that it does not mark emails as returned, that re-listing includes what wait_for_email already returned, the 7-day retention window, and the empty-inbox [] behavior. It even flags that sender/subject fields are untrusted data rather than instructions, which is valuable safety 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?

It is dense but front-loaded, leading with purpose, then output shape, then safety, then routing, then parameters. Each sentence carries information, though the length is at the upper end of what is necessary.

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 compensates by describing the returned array structure, the empty case, and retention limits. Combined with the annotations, an agent has everything needed to invoke and interpret this tool correctly.

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 the baseline is 3, but the description adds real meaning: out-of-range values are clamped (<=0 becomes 1, >50 becomes 50), no paging exists, and already-returned plus unread emails both count toward the limit. These counting and clamping semantics go beyond the schema's stated min/max.

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 and resource plus scope ('most recent emails in this inbox, newest first') and gives the exact return shape. It cleanly distinguishes itself from wait_for_email by explicitly naming that sibling. An agent can tell what this does without opening the schema.

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?

Explicit when-to-use ('find an email's id for read_email or delete_email, or to look up a code you already received') and when-not ('To wait for a new email use wait_for_email instead'). Both the positive and negative routing conditions are spelled out.

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