browser_fill

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

With no annotations, the description carries the full behavioral burden and does so well: it discloses auto-scroll and focus, that CSP-strict sites are handled via the Chrome Debugger API, that text selectors trigger an implicit click first, and that an unreachable element yields ok:false with error "covered". What is missing is whether the fill replaces or appends existing content and whether the value is set via native setter/input events, which matters for framework-bound forms.

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 sentences, front-loaded with the core action, then capabilities, then sibling routing, then the failure contract. Every sentence carries information, though the click-precondition sentence is dense enough that it could be trimmed slightly without losing meaning.

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?

There is no output schema, so the description compensates by documenting the failure shape (ok:false with error "covered"). Combined with capability disclosure and sibling routing, an agent has everything needed to invoke it correctly and interpret 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 coverage is 100%, so the baseline is 3, but the description adds real meaning beyond the schema: it clarifies that the selector accepts either CSS or text-based forms and explains the behavioral difference between them (text selectors are clicked first). It does not add anything for value, though that parameter is largely self-explanatory.

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 (fill a form input field with a value) and immediately carves out territory from siblings by naming browser_set_date and browser_set_combobox as the correct tools for date and combobox fields. An agent can distinguish this from browser_click, browser_select_option, and the other input-related siblings without opening a 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?

Explicit routing is given: date inputs go to browser_set_date, autocomplete/combobox to browser_set_combobox. It also states the precondition for success with text selectors (the element must be clickable at its center) and what happens when it is not, which tells the agent when to expect failure rather than a silent no-op.

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