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

With no readOnly or destructive hints in the annotations, the description carries the behavioral disclosure burden. It does so well by revealing that an explicit close drops the on-disk login snapshot for persistent sessions, while idle expiry keeps it. This is a meaningful side effect beyond what the schema or annotations convey.

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 sentences with no filler. The core action is front-loaded, and the second sentence adds only the critical distinction about persistent session snapshots. Every word 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 low-complexity, one-parameter close tool with no output schema, the description covers the action, resource impact, and a key side effect. It does not mention error behavior or idempotency, but these are not essential for an agent to invoke the tool correctly.

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?

The input schema already provides 100% coverage for the single session_id parameter with the description 'Session ID', so the baseline is 3. The description does not add parameter-level detail, but none is needed given the simple 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?

The description uses a specific verb ('Close') with a clear resource ('browser session') and a concrete consequence ('free its resources'). It clearly differentiates this from sibling tools like session_create or session_list, which serve different lifecycle stages.

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 intended usage is implied clearly: call this when a browser session should be ended and its resources released. The description adds useful context by contrasting explicit close with idle expiry, but it does not explicitly name alternatives or state when not to use the tool.

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