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

Adds substantial context beyond annotations: it discloses the two-phase lifecycle (start returns immediately, stop finalizes), the auto-stop behavior after max_seconds, that the download link persists after the Mac stops, a concurrency limit ('one recording at a time'), and a data-loss risk ('stopping the Mac deletes an unsaved one'). None of this is inferable from the annotations.

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?

Front-loaded with the purpose, then organized by action (start vs stop) followed by constraints. It is information-dense and mostly earns its sentences, though the middle is somewhat run-on with parenthetical asides.

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?

Despite no output schema, the description covers the return values of stop (length, size, url for browser, download_url for curl), the persistence of the link, and the full stateful lifecycle. An agent has everything needed to invoke start and stop correctly and to handle the results.

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 100%, so all five parameters (path, action, target, session_id, max_seconds) are already fully documented in the schema. The description restates target and max_seconds semantics but adds no new syntax or format detail beyond the schema, 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?

States a specific verb + resource: 'Records the Mac's screen as an MP4,' which is unambiguous and inherently distinguishable from the static-image sibling screenshot_mac. It stops short of naming or contrasting any sibling explicitly, so it falls just below a 5.

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?

Clearly explains the two operating modes: action start begins and returns at once, action stop saves and returns metadata. It gives the context for choosing start vs stop and screen vs simulator, but offers no guidance on when to use this tool instead of screenshot_mac or other capture tools.

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