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

Annotations already declare a non-destructive mutation, and the description adds real context: it touches only the read marker on the user's own profile and has no side effects on notes. It stops short of saying whether the call is idempotent or what happens for an unknown id, which keeps it from a 5.

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 compact sentences, front-loaded with the audience constraint and then the effect. No filler and no repetition of the schema.

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 one-parameter, non-destructive marker toggle with no output schema and full annotation coverage, the description supplies everything needed to decide and invoke correctly. The only minor omission is error behaviour for an invalid id.

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 the single 'id' parameter already documents 'omit to mark all as read'; the description's 'one item or all' merely restates that, adding no new syntax or format detail. 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?

States a specific verb+resource ('marks the user's Cobrain news (What's new) as read') plus the scope ('one item or all'), and explicitly contrasts with note tools ('never touches notes'), so an agent can separate it from siblings like app_note or find_notes.

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 an explicit when/when-not: 'Used only by the Cobrain app window (not by the model)' is a clear exclusion, and the alternative scope (one item vs all) is named inline.

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