Take screenshot

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

Annotations already cover readOnly/idempotent/no-destruction, and the description adds genuinely new behavioral context: the two-part return payload (JPEG then size/scale text line), the near-uniformly-dark-frame warning being advisory rather than a refusal, and the scale factor tying image pixels to logical coordinates.

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 tight sentences, front-loaded with what it does and what it returns, then usage routing and the caveat. No sentence is filler and the example output line is compact and illustrative.

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?

No output schema exists, yet the description fully specifies the return shape (image plus size/scale line) including a concrete example. Combined with the sibling routing and the coords="screenshot" handoff, an agent has everything needed to call it and consume 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?

Schema description coverage is 100%, so max_px, serial, and quality are already documented with ranges and defaults. The description adds no parameter-level detail beyond the cross-tool coords convention, which is baseline territory when the schema does 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+resource ("Take a screenshot of the device screen") and explicitly contrasts its role with adb_ui_dump, so an agent can separate it from siblings without opening any 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 explicit when-to-use routing: use ui_dump for labels/exact tap points, use the screenshot for what the dump cannot (images, video, games). It also names the downstream convention (coords="screenshot" on adb_tap/adb_swipe) that makes the output actionable.

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