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

Annotations already declare destructiveHint=true and openWorldHint=true, so the description's job is to add nuance — and it does: login state including cookies persists on disk, so the operation is reversible from a login standpoint even though it tears down the window. Gaps remain: nothing about what happens to open tabs/unsaved page state, or the error behavior when the named session does not exist.

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 sentences, front-loaded with the action, then persistence semantics, then the alternative tool. No filler and nothing repeated from the schema or title.

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-required-parameter lifecycle tool with full schema coverage and annotations, the description is essentially complete on behavior and routing. The only omission is return/error semantics (what a caller sees if the session is already closed), which is minor absent an output schema.

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 'session' parameter already documents its meaning and the 'default' fallback, so the description adds no parameter-level detail beyond referring to 'a web-automation session'. Baseline 3 applies when the schema carries the load.

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 and resource ('closes a web-automation session's window and frees it'), then explicitly names the sibling it is not (web_session_delete). An agent can distinguish it from web_login, web_navigate and web_session_delete without inspecting any schema.

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 the use case (close the window), the explicit exclusion ('closing does NOT clean up'), and routes to the correct alternative ('to erase a profile ... use web_session_delete'). It also states that web_login/web_navigate can reopen the session, which is exactly the decision-relevant follow-up.

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