Which process hosts which tab

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

readOnlyHint=true already declares the safety profile, and the description adds useful depth by naming the exact data source (osPid), implying one entry per tab. However, with no output schema it does not say what the response shape is, whether all windows or only the current one are covered, or how discarded/unloaded tabs appear.

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 core purpose is front-loaded in the first clause, followed by the implementation detail and then the use case. Three sentences, all short. The 'that name does not exist in Tabbrowser.sys.mjs' sentence is defensive filler for an agent, though it does prevent a bad API assumption.

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 zero-parameter, read-only introspection tool with no output schema, the description covers what it returns conceptually and why it matters. The remaining gap is scope (all windows vs. current window) and the exact return structure, which an agent would need before consuming 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?

The tool takes zero parameters and the input schema is an empty object, so there is nothing for the description to disambiguate. Baseline 4 applies; nothing is misrepresented.

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 the OS process id behind each tab, with the exact underlying property (browsingContext.currentWindowGlobal.osPid). It is clearly distinct from siblings like browser_list_tabs (tab enumeration) and browser_memory_usage (aggregate memory), so an agent can pick it without opening the schema.

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?

Gives concrete motivation: see how many content processes Firefox spun up, or whether two tabs share one. That is a clear usage context, but there are no explicit exclusions or named alternative tools (e.g. use browser_memory_usage for totals). The 'MEASURED: no gBrowser.getTabPids' note is anti-hallucination guidance rather than selection guidance.

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