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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open-world). The description adds genuinely useful behavior beyond that: classification is done 'from headers only (no bodies)', items carry reasons, and coverage is reported per account, plus the permission requirement 'Needs read; every plan'. This meaningfully informs the agent about data access and output character.

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 tightly packed sentences, front-loaded with what the tool does and its category output. The telegraphic final sentence 'Needs read; every plan.' is slightly terse but carries real prerequisite information without padding.

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 an output schema present, the description need not explain return values, and it covers purpose, category buckets, header-only scope, and the read requirement. For a read-only classifier this is nearly complete; only explicit sibling routing is absent.

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 description coverage is 80%, so the schema already documents limit, since, folder, and account. The description only echoes 'recent mail' and 'per account' without adding format or default details beyond what the schema provides, so the baseline of 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 (sorts) and resource (recent mail) and enumerates the exact output categories, so the agent knows precisely what it produces. It does not explicitly differentiate itself from siblings like awaiting_replies or digest, whose output overlaps with the waiting_on bucket, so it falls just short of a 5.

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?

Usage is implied (triage recent mail to decide what needs a reply) and the prerequisite 'Needs read; every plan' is stated, which is useful context. However, there is no explicit when-to-use versus awaiting_replies/digest/search, and no exclusions or conditions for choosing this over alternatives.

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