Lists frames with read access in an authorized Firefox tab, helping identify cross-origin frames that require separate permissions.
List frames with read access in an authorized tab. Cross-origin frames require their own permissions.
| Name | Required | Description | Default |
|---|---|---|---|
| tabId | Yes |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered. The description adds the non-obvious behavior that results are filtered by read access and that cross-origin frames are gated behind separate permissions — a real disclosure beyond the structured fields, though it omits what happens for an unauthorized tabId (error vs empty list).
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 short sentences with the scoping constraint front-loaded and no filler. The second sentence is a verbless fragment, but it stays readable and every clause carries information.
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 read tool with annotations covering safety and no output schema, most of the burden is met. Still missing: what identifies a frame in the result (so it can be passed to firefox_read_page or firefox_tab_action), whether the frame list is origin-filtered, and whether it includes the top frame.
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 description coverage is 0% for the single required tabId, so the schema gives only a name and integer type. The description partially compensates by stating the tab must be "authorized," implying tabId must come from firefox_list_tabs, but it adds no format or provenance detail beyond that hint.
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?
"List frames" gives a specific verb and resource, and "in an authorized tab" scopes it. It does not name or distinguish itself from any sibling, but no sibling overlaps directly (tab-level tools like firefox_list_tabs operate at a different granularity), so the purpose is still unambiguous.
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?
"Cross-origin frames require their own permissions" implies the prerequisite path (firefox_request_access) and explains why a frame may be absent, which is genuine when-to-use context. However, the alternative is never named, and nothing says when not to call this versus firefox_list_tabs or firefox_read_page.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.