mail_set_flags

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

Annotations already declare idempotent=true, destructive=false, and openWorld=true, so the safety profile is covered. The description adds meaningful domain behavior: the UID/UIDVALIDITY pairing requirement, the supported flag set, and the important exclusion that Deleted cannot be set here. It does not describe what happens on a UIDVALIDITY mismatch, which keeps 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?

Three tight sentences, front-loaded with the action, then supported values, then the exclusion. No filler, though the value enumeration could be folded more economically.

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 6-parameter mutation with no output schema, the description covers the flag domain and the Deleted exclusion well, but omits the semantics of accountId/folder, whether add and remove may be combined in one call, and any note on failure modes. Adequate but with clear gaps.

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 parameter meaning, and it partially does: it explains that add/remove take flag names and enumerates valid values (Seen, Answered, Flagged, Draft, custom keywords). However, accountId, folder, and uidValidity are never explained, and the required-vs-optional distinction is left to the schema.

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 (add/remove) and resource (message flags) and immediately distinguishes itself from the deletion siblings by pointing to trash/permanent delete tools. An agent can identify the operation 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?

Gives a clear operational condition (use the exact UID and observed UIDVALIDITY) and an explicit when-not with alternatives (Deleted is excluded; use trash or permanent delete tools). It lacks guidance on when to reach for this vs. other flag-adjacent operations, but the routing to the delete siblings is explicit.

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