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

Annotations already declare non-read-only, non-destructive, and idempotent behavior. The description adds non-obvious details: cookies are preserved, the browser goes to sleep, the per-minute charge stops, and it returns the session's minutes and credits. This is valuable context beyond what the annotations provide.

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?

The description is two concise clauses with no wasted words, front-loading the action and then the key effects. Every sentence earns its place.

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 zero-parameter close tool with annotations covering safety, the description provides everything an agent needs: the action, state preservation, billing impact, and return values. No output schema exists, so mentioning the returned minutes and credits is appropriate and useful.

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?

There are zero parameters, so no parameter semantics are needed. The baseline score for a tool with no parameters is 4.

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 states a specific verb and resource: 'Ends the session in the user's Substack Cloud Browser.' This clearly distinguishes it from sibling browser tools like open, navigate, and click, which all interact with an active session rather than ending it.

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 description provides clear context for when to use it: to stop the per-minute charge while preserving cookies. However, it does not explicitly state when not to use it or name alternatives, leaving some inference to the agent.

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