browser_fill_form

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

With no annotations provided, the description carries the full behavioral burden. It adds useful context about batching ('in one call') and a reliability/performance comparison to browser_type, but it does not disclose whether existing field values are replaced or appended, how missing refs are handled, or what the tool returns on success or failure.

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 totaling roughly 30 words, with the core purpose front-loaded and no filler. The parameter convention and the comparison to browser_type each earn their place in a compact definition.

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 single-parameter tool the definition covers purpose, input shape, and usage context, but with no output schema and no annotations it omits the return value, error behavior, and the meaning of ref. An agent calling this tool has enough to attempt a call but not enough to handle failures or validate inputs confidently.

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 0%, so the description must compensate, but 'Pass fields as an array of {ref, text}' merely restates what the input schema already defines. It does not explain what a ref is (selector, accessibility id, snapshot reference) or how an agent should obtain valid ref values, leaving the key parameter semantically ambiguous.

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: 'Fill multiple fields in one call.' It clearly states the batch nature of the operation and distinguishes it from the sibling browser_type by claiming it is faster and more reliable for forms. An agent can tell what this tool does 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?

The description names browser_type as the alternative and gives the selection condition ('for forms'), providing clear context for when the batch call is preferable. However, it does not state explicit when-not conditions, such as using browser_type for a single field or browser_fill_secret for sensitive values.

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