Unread summary

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

Annotations already declare readOnly=true, idempotent=true, destructive=false. The description adds valuable behavioral traits: mailboxes with zero unread are omitted, it reads counters only (fast on large mailboxes), and it returns a specific structured summary. These traits are not in annotations, and there is no contradiction.

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?

The description is three sentences, each earning its place: the first states purpose, the second explains filtering and performance, and the third gives the return format. There is no filler or repetition; it is front-loaded with the most important 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?

Given the tool's simple scope (one optional param), strong annotations, and an inline return schema in the description, everything needed to decide and invoke the tool correctly is present. The description covers purpose, behavior, and output format without missing critical information.

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?

The input schema already describes the only parameter 'account' with 100% coverage, including examples and the note that omitting it spans all accounts. The description does not add parameter-level detail beyond that, so the schema itself carries the information. This aligns with the baseline 3 for high schema coverage.

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 clearly states the tool's function: 'Unread counts per account and mailbox' with a concrete verb and resource. It distinguishes itself from message-level tools by calling it the 'cheapest way to answer what's waiting for me', implying a summary query rather than message retrieval.

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 description gives clear context on when to use it (quick unread summary) and explicitly contrasts with scanning messages ('does not scan messages'), implying search or get message tools for content. However, it doesn't name alternative tools explicitly in the description, so it stops short of full exclusion guidance.

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