session_press

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

Beyond the annotations (readOnlyHint=false, destructiveHint=true), the description adds valuable behavioral details: it returns '{pressed}' naming the key, and it discloses the exact error behavior ('anything else fails with the supported list rather than doing nothing'). It also explains the focusing behavior ('or on a named element after focusing it'), which is not evident from the schema alone. No contradiction with annotations exists.

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?

The description is compact and front-loaded with the core action, followed by purpose examples, return value, and supported keys/error behavior. Each sentence serves a distinct function with no filler. The structure quickly informs an agent what the tool does, when to use it, and what to expect.

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 tool with four parameters, one required, no output schema, and annotations already providing safety semantics, the description covers the essential behavioral context: focus targeting, return value, supported keys, and failure mode. The schema covers parameter details and tab/selector behavior, so nothing critical is missing for correct invocation.

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 the schema already documents all four parameters. The description reinforces the meaning of the key parameter by listing supported keys and clarifies the selector/ref use case ('on a named element after focusing it'), but it does not add substantial detail beyond the schema. Baseline 3 is appropriate because the schema carries the semantic weight.

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 uses a specific verb and resource: 'Press a single keyboard key on the focused element, or on a named element after focusing it.' It clearly identifies the tool as a key-press operation and distinguishes it from sibling tools like session_click and session_type by its focus on keyboard keys. The concrete use cases (submit form with Enter, dismiss dialog with Escape, walk suggestion list with ArrowDown) reinforce the tool's unique purpose.

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 provides explicit use cases: 'Use it to submit a form with Enter, dismiss a dialog with Escape, or walk a suggestion list with ArrowDown.' This gives clear context for when the tool is appropriate, though it does not explicitly mention when not to use it or name alternative tools. Because the examples imply the alternative (typing full text with session_type, clicking with session_click), the guidance is strong but not exhaustive.

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