fill_form

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

readOnlyHint=false already tells the agent this mutates page state, and the description correctly reinforces that by describing the fill action plus a concrete example. However, it never says what happens on partial failure (do earlier elements stay filled?), whether values are validated, or that element uids must come from a prior snapshot. Its remaining content is a speed/reliability pitch rather than new behavioral fact.

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?

Three short sentences, front-loaded with the capability, then the selection rule, then a concrete example. The middle sentence's 'significantly faster, more reliable, reduces turn count' is a mild sales pitch, but it is directly actionable guidance for tool selection.

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?

No output schema exists, so the description should cover the response: includeSnapshot partially explains this, but the description is silent on what a successful fill returns and on the prerequisite of obtaining uids via take_snapshot. Those two omissions are the only meaningful gaps for a 3-parameter mutation tool.

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 pageId, elements[].uid, elements[].value, and includeSnapshot. The description adds only the illustrative username/password/'Remember Me' example, which hints at the array's batch shape but doesn't explain includeSnapshot or the checkbox/radio string conventions the schema handles.

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?

States a specific verb (fill out) and resource (multiple form elements) and enumerates the element kinds covered (inputs, selects, checkboxes, radios). It also explicitly positions itself against the sibling tools 'fill' and 'click', so an agent can distinguish it from them without opening any 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?

Gives an explicit always-use rule with named alternatives: prefer this over multiple individual 'fill' or 'click' calls when interacting with forms. The converse case (use 'fill' when only a single element is targeted) is only implied rather than stated.

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