iOS Simulator: Screenshot

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

Beyond the readOnlyHint annotation, the description discloses the key behavioral traits: default scaling to device point size, the resulting coordinateSpace metadata ('points'), the shift to image_pixels when max_dimension is overridden, and the fact that save_path writes a full-resolution PNG while 'the returned image is still the downscaled one.' This is exactly the kind of non-obvious behavior an agent needs to interpret results correctly.

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?

Four sentences, each earning its place: core purpose, the critical coordinate-space behavior, sibling complementarity, and workflow rule. The most decision-relevant fact (tap-coordinate compatibility) is front-loaded in sentence two. No filler, no repetition of schema content.

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 having no output schema, the description conveys the return semantics that matter (image plus coordinateSpace metadata), and the schema handles the four optional parameters exhaustively. The readOnly annotation covers the safety profile. Nothing an agent needs to invoke this correctly — coordinate systems, sibling relationships, workflow cadence, parameter trade-offs — is missing.

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%, so the baseline is 3 — and indeed the schema's per-parameter descriptions are rich on their own. The main description adds one genuinely additive semantic: the default scaling means 'a position read off this image can be passed straight to ios_simulator_tap with no conversion,' which gives the default parameter behavior a concrete cross-tool consequence not stated in the schema. This nudges it above baseline.

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?

The description states a specific verb and resource — 'Capture the screen and return it as an image' — and immediately distinguishes itself from the closest sibling, ios_simulator_ui_tree: 'the image shows you what the screen looks like, the tree gives you exact labels and identifiers.' An agent can tell exactly what this tool does and how it differs from alternatives.

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 gives explicit pairing guidance: 'Pair it with ios_simulator_ui_tree rather than choosing between them,' complete with the reason for each tool's role. It also prescribes a workflow rule ('Re-screenshot after every action rather than chaining blind taps') and the device parameter description further advises when to omit it. This is actionable usage direction, not just a vague context hint.

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