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browser_fill

Fill a form input value via CDP, handling React/Vue/Svelte controlled inputs that bypass standard JS value assignment. Use after obtaining a stable selector via browser_overview or browser_locate.

Instructions

Fill a form input with a value via CDP — works on React/Vue/Svelte controlled inputs that reject browser_eval value assignment. Use browser_overview or browser_locate first to obtain a stable selector. Use this over browser_eval when setting a controlled input's value via JS does not update the framework state. Caveats: Requires browser_open (CDP active). Does not work on contenteditable rich-text editors — use keyboard(action='type') for those. actual in response shows what the element's value property reads after fill; verify it matches the intended value.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
selectorYesCSS selector for the target element (e.g. '#submit', '.btn', 'button[type=submit]').
valueYesText to fill into the input element
tabIdNoTab ID from browser_open. Omit to use the first page tab.
portNoChrome/Edge CDP remote debugging port.
includeContextNoWhen true, append activeTab and readyState context to the response.
includeNoOptional response-shape opt-in. `['envelope']` returns the self-documenting envelope (`_version` / `data` / `as_of` / `confidence`). `['raw']` forces raw shape (overrides DESKTOP_TOUCH_ENVELOPE=1 server default). Default behaviour is raw shape (compat with existing clients).
Behavior4/5

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

With no annotations, the description fully covers behavior: uses CDP, prerequisite browser_open, effect on controlled inputs, and mentions the 'actual' response field. Lacks only minor edge-case details.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Concise and well-structured: purpose first, usage guidelines, then caveats. Every sentence adds value without redundancy.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given 6 parameters and no output schema, the description covers prerequisites, usage, limitations, and response details (actual field). Adequate for effective tool invocation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so baseline is 3. The description adds context about stable selectors and controlled inputs but does not significantly enrich parameter meaning beyond schema descriptions.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool fills form inputs via CDP, specifically for React/Vue/Svelte controlled inputs, distinguishing it from browser_eval.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides explicit instructions to obtain a stable selector first and to use this tool over browser_eval for controlled inputs. Includes caveats about requirements and alternatives for contenteditable.

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

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