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

Annotations already declare readOnlyHint=false, idempotentHint=true, destructiveHint=false, so the safety profile is covered. The description adds real value by stating the visible state change (changes stop appearing as new on the account page), but says nothing about whether marking is reversible, whether already-seen ids error, or what the response contains.

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?

A single front-loaded sentence with the effect stated up front and no filler. The parenthetical is compact and functional, though it slightly compresses information that could have been clearer as a clause.

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?

With two optional parameters, full schema coverage, and annotations carrying the safety profile, the description covers the core scope and outcome. Only minor gaps remain around the return value and error behavior, which are low-stakes for a no-output-schema, idempotent mutation.

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% and both parameters carry their own descriptions with scope and omission behavior. The description's '(some, by id, or all)' parallels the schema without adding format or edge-case detail, so the baseline 3 applies.

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 and resource ('Marks a folder's changes seen') and adds the observable outcome ('stop showing as new on the account page'), so the effect is unambiguous. It does not explicitly distinguish itself from any sibling, though no listed sibling performs this action, so the gap is minor.

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 parenthetical '(some, by id, or all)' implies the two operating modes, and the omission semantics are inferable, but there is no explicit when-to-use versus when-not guidance, no prerequisites, and no named alternatives. Usage is implied rather than stated.

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