ui_fill

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

No annotations are provided, so the description carries the behavioral disclosure burden. It does this well by stating that the tool fires the 'input' and 'change' events the application listens for, and that it is fast because it bypasses per-keystroke typing. It does not mention return/error behavior or permission requirements, but the core hidden behavior is disclosed.

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?

Two sentences deliver the action, the side effect, the performance characteristic, and the alternative tool. There is no filler, and the most important behavioral facts are front-loaded.

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 10 parameters and no output schema, the description covers the primary behavior, event side effects, and sibling differentiation, while the schema covers parameter semantics. It leaves return-value and failure-mode behavior to inference, which is a minor gap given the otherwise rich schema and clear description.

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 explains every parameter. The description reinforces the meaning of 'value' by saying it sets the field's value and fires events, but it does not add material parameter-level detail beyond what the schema provides. The baseline of 3 is appropriate.

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 opens with a specific verb and resource: 'Set the value of a text field, textarea or contenteditable in one step'. It also explicitly contrasts with ui_type by noting this tool does not type character by character, so an agent can distinguish it from its closest sibling without opening schemas.

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 an explicit routing rule: use ui_type instead when a field reacts to each keystroke, such as a typeahead or autocomplete. This tells the agent both when to use this tool and when to prefer an alternative.

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