Open an extension's toolbar popup

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

The description goes well beyond the readOnlyHint=false annotation by disclosing the mechanism: opening the unified-extensions panel, locating the entry by id, and clicking the action button. It also notes the popup URL is reported, preventing silent-failure confusion. It stops short of noting residual side effects, such as the panel remaining open or focus changes.

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?

Three sentences, front-loaded with the action and its user-visible equivalent, then the constraint and mechanism. Dense but every sentence carries information; only the mechanism detail could be trimmed slightly.

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?

With a single required parameter, a full-coverage schema, and no output schema, the description supplies what is missing: the underlying UI mechanism and the fact that a popup URL is returned. An agent has enough to call it and interpret the result.

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 only parameter ('id', extension id) is self-explanatory. The description ties the id to locating the matching toolbar item, but adds no format or constraint details beyond the schema, so baseline 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?

The description opens with a specific verb and resource ('Open the browser-action popup of an extension') and grounds it in a familiar equivalent ('the same thing clicking its toolbar button does'), which clearly separates it from siblings like browser_open_extension_options and browser_close_extension_popup.

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?

It explains why this UI-driven path exists (Firefox does not expose extension.browserAction to remote scripts), which implies when it must be used, but it never names alternatives such as browser_run_in_extension or browser_open_extension_options, nor states exclusions.

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