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form_input

Populate textboxes, checkboxes, dropdowns, and other form controls in a Firefox page via a ref from read_page, triggering native input/change events for React compatibility.

Instructions

Fill one form control that read_page has already tagged with a ref, without aiming a click at it. ref, value and tabId are all required. Text boxes, textareas, number and date fields, contenteditable regions, checkboxes, radios and dropdowns are covered; a file input is not, and goes through file_upload or upload_image, which read only from the directories this server is allowed to open. The write goes through the element's native setter and is followed by input and change events, while checkboxes and radios are toggled with a real click, so React and its relatives notice the change. A dropdown is matched against option values first, then against the labels shown to the user, ignoring case on a last pass; when nothing matches, the error lists the options that exist. Disabled controls are turned down. A ref lives only as long as the node behind it, so after a navigation, a reload, or a re-render that swaps the element out, run read_page again or this fails with an unknown-ref error.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
refYesThe element id read_page handed out, shaped like ref_1 or ref_2. It names one live node, so take it from the most recent read of this page; older ids are usually stale.
tabIdYesThe tab holding the element; required. Ids come from tabs_context_mcp, and the ref has to belong to that same tab's document.
valueYesWhat the control should end up holding. Text-like fields take a string or a number. Checkboxes and radios take true or false (an empty string, or "false", "no", "0", "off", also reads as unchecked). A dropdown takes either the option's value attribute or the label the user sees. Arrays and objects are rejected instead of being stringified into the field.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.2.0

TDQS

A4.8/5.0
Behavior5/5

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

With no annotations, the description fully covers behavior: native setter, input/change events, real clicks for checkboxes, dropdown matching logic, disabled control handling, and staleness errors. This gives a complete picture of side effects and failure modes.

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?

The description is detailed yet tightly organized, with each sentence conveying necessary information without redundancy. The main action and requirements are front-loaded, followed by control-specific semantics and edge cases.

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?

The description covers all relevant operational details: how to obtain the ref, how to pair it with a tab, how values map to controls, what happens with invalid inputs, and when errors occur (stale ref, disabled, unmatched dropdown). It is complete for an agent to use correctly.

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

Parameters5/5

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

Even though schema coverage is 100%, the description adds significant nuance beyond the schema: it clarifies stale refs, tab ownership, accepted value types per control, and rejection of arrays/objects. This meaningfully enhances understanding beyond the raw property definitions.

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 a form control using a ref from read_page, and explicitly distinguishes it from clicking. It enumerates supported control types, making the purpose unambiguous.

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

Usage Guidelines4/5

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

It states required parameters and gives detailed guidance on ref freshness, tabId association, and value semantics per control type. It contrasts with file upload tools but does not explicitly enumerate all alternative tools or conditions for choosing this one over them, though the context is largely sufficient.

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