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

Annotations already declare this is a non-read-only, non-destructive, non-idempotent mutation, so the safety profile is covered. The description usefully adds that the state change is reversible (unread with ids) and gives the return shape `{ unread }`, but it does not address the non-idempotent hint or how overlapping selectors (ids + kinds + all) interact.

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?

Two tight sentences that front-load the primary operation and its three modes, then the exceptional reverse case, then the return value. Every clause carries information; nothing is redundant.

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 four-parameter mutation with no output schema, the description supplies the selector semantics, the reversal path, and the returned field, which is close to sufficient. The remaining gap is behavior with zero selectors, since all parameters are optional and `all` presumably defaults to something unspecified.

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 100%, but the schema descriptions are terse ('Everything.', 'Which ones.', 'A filter's worth.'), so the description meaningfully adds that `unread` is only meaningful together with `ids` — a cross-parameter constraint the schema cannot express. It does not mention the 200-item cap on `ids` or precedence rules.

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?

The description gives a specific verb ('Mark ... read') and resource ('your notifications'), and enumerates the three selection modes (ids, kinds, all) so the agent knows exactly what the tool operates on. It stops short of naming a sibling such as mark_conversation_read or list_notifications to disambiguate the notification scope explicitly.

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?

It clearly explains how to drive the tool: pass `ids` for a subset, `kinds` for a category, or `all: true` for everything, and it documents the reverse path via `unread: true` with `ids`. What's missing is guidance on when to choose this over list_notifications or count_unread_notifications, and what happens when no selector is supplied.

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