Open or close the downloads panel

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

readOnlyHint=false already tells the agent this mutates UI state, so the bar is lower. The description adds that it returns whether the panel is currently showing, which is valuable given no output schema, but it omits what happens if the panel is already in the requested state and offers no side-effect or scope notes. The 'MEASURED: DownloadsPanel.showPanel() / hidePanel()' clause documents an internal browser API rather than agent-facing behavior.

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?

Only two sentences and the purpose is front-loaded, which is good. But the middle 'MEASURED: ... NOT .show(), which does not exist' clause is internal implementation trivia that does not help an agent decide or call correctly, and it interrupts the flow between purpose and return behavior.

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 UI toggle with no output schema, the description covers what it does, what the parameter means, and what it reports back. Only the already-open/already-closed behavior and interaction with the downloads list tools are missing.

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 boolean already carries 'true to open, false to close'. The description adds nothing beyond the schema about the parameter, so the baseline of 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?

Specific verb (open/close) plus a specific resource (the downloads panel), with a helpful parenthetical identifying it as the toolbar arrow listing recent downloads. That locates it clearly apart from browser_list_downloads, though no sibling is named explicitly.

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?

Usage is only implied by the 'open or close' phrasing and the boolean parameter; there is no statement of when to reach for this versus browser_list_downloads, browser_download_manage, or browser_download_add. The closing note about reporting current state hints at a read use case but does not spell it out.

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