Extension details: options page, popup, sidebar

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

Annotations already declare readOnlyHint=true, so safety is covered; the description adds real behavioral value by stating the data is read from the live manifest and warning that AddonManager.optionsURL is null for MV3 extensions using options_ui. It does not cover failure behavior for an unknown/invalid id, which keeps it short of a 5.

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 outcome and followed by the implementation caveat. Every clause carries information; nothing is redundant with the title or annotations.

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 no output schema, the description usefully enumerates the three reported fields, and the manifest-source note explains where values come from. It stops short of describing return shape (e.g., nulls when no popup/sidebar exists) or error behavior, which would fully close the gap.

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 parameter is documented ('Extension id'), so the schema does the work. The description adds no extra meaning about the id format (GUID vs slug) or how to obtain it, which is the baseline expectation when coverage is high.

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 ('Report what UI entry points an extension actually exposes') and enumerates exactly what is returned: options page URL, browser action popup, sidebar panel. This clearly distinguishes it from siblings like browser_open_extension_options (which opens rather than reports) and browser_list_sidebars (which lists sidebars globally, not per-extension).

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 implies a discovery/inspection use case and hints at why you'd want it (MV3 options_ui cases), but never says when to use it versus browser_open_extension_options, browser_list_addons, or browser_extension_permissions. No explicit exclusions or alternative routing are provided.

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