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

The description goes beyond the sparse annotations by disclosing that closing does not delete the saved login, that cookies persist on disk, and that the session can be reopened without signing in. It also warns that closing is not a cleanup operation, which is critical behavioral context not present in readOnlyHint/destructiveHint.

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 compact and well-structured: the first sentence states the core action, and the second sentence delivers the crucial persistence caveat and the deletion alternative. No sentence is wasted, and the most decision-relevant information (session persists after close) is front-loaded.

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 simple one-parameter session close operation with no output schema, the description covers the key contextual facts: what is closed, what persists, how to reopen later, and how to permanently delete. The contrast with web_session_delete gives the agent enough context to choose correctly among the web_session siblings.

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 schema already fully documents the single 'session' parameter with its type, description, and default. The tool description does not add parameter-level detail, but with 100% schema coverage the baseline of 3 applies; the description's mention of named login profiles indirectly reinforces the parameter's meaning without adding new syntax or format guidance.

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 action ('Closes a web-automation session's window and frees it') and names the resource (a web-automation session). It also explicitly contrasts with web_session_delete by clarifying what closing does NOT do, which distinguishes it from the most similar sibling.

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 clearly indicates when to use this tool versus alternatives: use it to close a session while preserving login credentials, and use web_session_delete when the profile should be erased. It also notes that web_login/web_navigate can reopen the session later without re-authenticating, giving an agent concrete routing guidance.

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