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

Annotations only supply the generic safety profile (destructive, non-idempotent, not read-only); the description adds real behavior the annotations cannot convey: it creates and subscribes a junk folder when absent, refuses already-junked messages, preserves flags and original dates, requires a single source folder, and triggers server-side spam training. It does not describe response payload shape beyond 'the reply says so', but the behavioral disclosure is well above the annotation baseline.

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?

Front-loaded with purpose, then constraints, then the sibling pointer — a sensible order. It is on the long side and leans on all-caps emphasis for the folder-creation behavior, which is slightly noisy, but each sentence carries distinct 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?

For a destructive, side-effectful batch operation with no output schema, the description covers the essentials: folder resolution by role across M365/Gmail/IMAP, creation-if-missing with subscription, refusal semantics, preservation guarantees, and batching. An agent has everything needed to call it safely and 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 description coverage is 100%, so both parameters are already documented, including the batching guidance the description repeats verbatim in its final sentence. The description's only genuine addition is the same-source-folder constraint, which touches the mailbox parameter but is framed behaviorally rather than as parameter syntax, so the baseline 3 holds.

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+resource ('Move messages into the junk folder') and anchors it to a familiar mental model ('what "report spam" does in a mail client'), which cleanly separates it from siblings like move_email. It also names not_junk as the inverse, so an agent can route correctly without opening a 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 (spam reporting / filter training), when-not (messages already in the junk folder are refused), an alternative (not_junk reverses this), and an operational constraint (all messages must share one source folder, batch UIDs in one call). Nothing important is left to inference.

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