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

Goes beyond the annotations by disclosing idempotent behavior explicitly ('calling it again on an already-read notification still returns success'), the feature dependency (Notification Center), and the 404 failure mode when it is disabled. It does not explain the destructiveHint=true annotation, though for a mark-as-read operation that is largely self-evident.

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-loads the core action in the first sentence and layers on idempotency, parameter guidance, and the feature/error constraint in a tight, well-ordered block. Dense but no sentence is wasted.

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?

Covers the operation, its idempotency, the parameter contract, and the 404 failure condition, which is sufficient given there is no output schema. It stops short of describing any success payload shape, but the description explicitly says it returns success, which is enough for an agent.

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 schema only names `openedFrom` without describing it; the description supplies the meaning (the channel the reader came through), the value semantics, the relationship to `notificationSource` on external links, and the omission condition. This substantially compensates for the 50% 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?

States a specific verb (mark as read) and resource (a single notification) scoped to the authenticated user. It is clearly distinguishable from sibling tools markAllNotificationsRead and markNotificationBatchRead by virtue of operating on one notification.

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 explicit guidance on when to supply `openedFrom` versus when to omit it, and ties the enum values to the reader's entry channel. It does not, however, name the sibling alternatives (markAllNotificationsRead, markNotificationBatchRead) or state when one should be preferred over this one.

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