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

Annotations already declare readOnly/non-destructive/non-open-world, so the safety profile is covered. The description adds real behavioral context beyond annotations: the Mac Screen Recording permission requirement and the lossy-vs-lossless tradeoff between jpeg and png. It does not disclose what is returned (path, base64, dimensions), which would complete the picture.

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 short sentences, zero filler, front-loaded with the core action followed by the alternative-tool routing. Every clause carries information an agent can act on.

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 simple read-only capture tool with three optional params and no output schema, the description covers the action, format tradeoff, permission prerequisite, and sibling alternative. The one gap is the return shape (no output schema exists to explain it), which would matter for handling the captured image.

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 67%, with deviceId and workSessionId already documented in the schema and format's enum/default declared. The description only adds 'png for lossless' on top of the enum, which is marginal. Baseline 3 is appropriate given the schema does most of the work.

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 ('Capture the computer's screen as a JPEG image') plus a scope qualifier (whole computer screen, not browser content). It explicitly names the sibling browser_snapshot and the case where that sibling is preferable, so an agent can distinguish them without opening either 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 clear context: use for the computer screen generally, use browser_snapshot for web pages in the connected browser, and note the Mac permission prerequisite. It stops short of saying when this tool should NOT be used at all (e.g., multi-monitor selection), so it is strong but not fully exhaustive.

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