browser_fill

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

With no annotations, the description carries the full burden and it delivers meaningful behavior: auto-scrolling, focusing the element, and working on CSP-strict sites via the Chrome Debugger API. It doesn't mention potential side effects like overwriting existing values or triggering events, but the disclosed traits go well beyond a minimal description.

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 efficient: a one-line purpose, two capability notes, and a two-item routing sentence. Every sentence earns its place, and the core action is front-loaded before alternatives.

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 simple two-parameter tool with no output schema, the description covers the essential use context: why it exists, what behaviors it performs, technical limitations it handles (CSP), and alternatives for edge cases. Minor gaps like error behavior or event triggering are not critical for a fill operation, so this is almost fully complete.

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%, with both 'selector' and 'value' already documented. The description repeats the selectors info but adds little beyond what the schema states. Baseline 3 applies because the schema does the heavy lifting and the description does not materially enhance parameter understanding.

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 clear verb and resource: 'Fill a form input field with a value.' It explicitly differentiates from nearby siblings by naming browser_set_date for date inputs and browser_set_combobox for autocomplete/combobox controls, so an agent can tell them apart 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 provides explicit routing: 'For date inputs use browser_set_date, for autocomplete/combobox use browser_set_combobox.' It also clarifies the accepted selector types (CSS and text-based), helping the agent decide when this tool is appropriate. This is direct when-to-use guidance with named alternatives.

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