browser-firefox-mcp

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fill_input

Fill a form field by CSS selector with a value, clearing existing input and firing framework-compatible events. Set a timeout for element readiness to ensure reliable automation in security testing.

Instructions

Fill a form field. Fires framework-compatible input/change events.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "selector": "<selector>",
      "value": "<value>"
    },
    "name": "fill_input"
  }
}

Input Schema

Name	Required	Description	Default
`value`	Yes
`timeout`	No
`selector`	Yes
`clear_first`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Aug 20, 2026

TDQS

B3.3/5.0

Behavior3/5

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

No annotations are provided, so the description carries the burden of behavioral disclosure. It does disclose an important non-obvious behavior: firing framework-compatible input/change events. However, it omits other meaningful behaviors such as the default clear_first behavior, timeout handling, and limitations around non-form elements, leaving clear gaps.

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 two short sentences with no filler. It front-loads the core action and then adds a valuable, non-redundant behavioral detail about event firing.

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

Completeness2/5

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

Given four parameters, no annotations, and no output schema, the description is not complete enough. It does not explain timeout behavior, clear_first semantics, supported element types, or failure modes, which an agent would need for reliable invocation.

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

Parameters2/5

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

Schema description coverage is 0%, and the description adds no parameter-specific meaning for selector, value, timeout, or clear_first. It only provides general context that the tool targets form fields, so it does not compensate for the missing parameter documentation.

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 a specific verb and resource: 'Fill a form field.' It also adds the behavioral detail of firing framework-compatible input/change events, which distinguishes it from sibling interaction tools like click, press_key, or upload_file.

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

Usage Guidelines2/5

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

There is no guidance on when to use this tool versus alternatives such as click_text or press_key. It does not mention exclusions, prerequisites, or scenarios where a different interaction tool would be more appropriate.

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