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

Annotations already declare destructiveHint=true, idempotentHint=true, readOnlyHint=false, so the mutation safety profile is covered by structured data. The description adds a real behavioral constraint not in the annotations: foreign notification IDs are rejected, i.e. ownership/authorization is enforced. It does not add anything on idempotency or response behavior, but that is already structured.

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 short sentences: action, constraint, alternative. Front-loaded action statement, zero filler, every sentence carries 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?

An output schema exists, so return values need not be explained. For a one-parameter mutation tool, the description covers the action, the ownership constraint, and the sibling alternative — nothing an agent needs to call it correctly is missing.

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% and the single parameter's description already points to its source ('id from get_notifications'), so the baseline is 3. The description restates ownership semantics for the ID but adds no syntax, format, or sourcing detail beyond 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 and resource ('Mark one of the signed-in user's notifications as read') and scopes it to the signed-in user's own notifications. It also names the sibling tool it is not, so an agent can distinguish it from mark_all_notifications_read without opening either 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?

Explicitly routes the agent to mark_all_notifications_read for the bulk case, and states the exclusion condition ('IDs that are not the signed-in user's notifications are rejected'). Both when-to-use and when-not-to-use are covered.

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