glass_drag

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

Annotations only carry basic hints (readOnly=false, destructive=false), so the description carries the behavioral burden and delivers richly: window-relative vs screen-relative coordinate semantics, the press-move-release lifecycle in steps over duration_ms, default button behavior, modifiers held throughout, and the safety behavior that out-of-window endpoints are refused with an error reporting window size. No contradiction with 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?

Dense but every sentence earns its place: coordinate semantics, mechanics, defaults, error behavior, use cases, alternatives, and batching guidance. The most decision-relevant fact (window-relative coordinates disambiguating 0,0) is front-loaded, and the sibling routing is compactly appended.

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 7-parameter, 4-required tool with no output schema, the description covers the key behavioral surface an agent needs: coordinate frame, execution lifecycle, defaults, modifier handling, out-of-bounds refusal, and alternative-tool routing. No critical call-time decision is left undocumented.

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 baseline is 3. The description adds value beyond the schema by explaining how duration_ms shapes motion ('moves across in steps'), the default button behavior, and how modifiers apply ('held throughout'), plus the endpoint-validation constraint tying x1/y1/x2/y2 to the window bounds. This is genuine added meaning, not mere restatement.

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?

Opens with a specific verb+resource: 'Drag with a button held from (x1,y1) to (x2,y2)'. It explicitly differentiates from siblings — glass_gesture (multi-touch pinch/rotate), glass_click (press-and-release in place), and glass_do (batching). An agent can tell exactly what this tool does and what it is not 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 explicit selection criteria: 'Use this for a single pointer — selecting text, moving an item, resizing a pane', then names the alternatives with their distinguishing conditions (glass_gesture for 2+ pointers, glass_click for in-place press/release, glass_do when two or more next actions are known). The when/when-not/alternatives guidance is complete and leaves nothing to inference.

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