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

Annotations already declare idempotentHint=true and destructiveHint=true, so the safety profile is partly covered. The description adds genuinely useful behavior beyond that: deduplication of duplicate IDs, silent ignoring of missing or foreign IDs, and a null return with no per-item reporting — all of which affect how an agent interprets success.

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 and immediately followed by constraints and return behavior. No filler and nothing buried.

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?

An output schema exists and the description still clarifies the return shape (result:null, no per-item reports), and mutation edge cases are covered. The notable omission is any framing of how this relates to its singular and all-notifications siblings, which matters given destructiveHint=true.

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 0%, so the description carries the burden. It does well on notificationIds (at least one required, duplicates deduplicated, missing/foreign ignored), but the 'seen' boolean is never explained — whether false unmarks as unseen is left to inference.

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 ('Set seen on selected notificationIds') plus scope ('in your inbox'). The word 'selected' implicitly distinguishes it from updateNotificationSeen (single) and updateAllNotificationsSeen (all), but it never names those siblings explicitly, so an agent must infer the distinction.

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 implies a batch-selected use case, but gives no explicit when-to-use rules and never names updateNotificationSeen or updateAllNotificationsSeen as the alternatives. The agent can guess from 'selected' but must reason it out rather than being routed.

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