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Fast Browser MCP

Fast Browser MCP

by kqlio67
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Local

browser_fill

Fills input fields with text using a snapshot reference or CSS selector and auto-detects contenteditable and rich text editors.

Instructions

Fill text into an input element by its snapshot reference (@1, @2, ...) or CSS selector. Auto-detects contenteditable and rich text editors.

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": {
      "text": "<text>"
    },
    "name": "browser_fill"
  }
}

Input Schema

NameRequiredDescriptionDefault
refNoReference from snapshot (e.g. '@1')
textYesText to enter
clearNoClear before typing
pasteNoUse instant CDP text insertion pipeline
selectorNoCSS selector if ref is not used
press_enterNoPress Enter key immediately after entering text (useful for chat submissions or search queries)

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changedv0.12.0
    • addedInput schema / properties / paste
      Added value: +{
+  "default": false,
+  "description": "Use instant CDP text insertion pipeline",
+  "type": "boolean"
+}
    • addedInput schema / properties / press_enter
      Added value: +{
+  "default": false,
+  "description": "Press Enter key immediately after entering text (useful for chat submissions or search queries)",
+  "type": "boolean"
+}
  2. First observedv0.8.0

TDQS

B3.4/5.0
Behavior3/5

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

No annotations are provided, so the description carries the full burden. It does add real behavioral context ('auto-detects contenteditable and rich text editors'), but omits what happens on a missing ref/selector, whether the element is scrolled into view or focused, and whether typing is dispatched as real key events.

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

Conciseness4/5

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

Two tight sentences with the core action front-loaded and zero filler. It is efficient, though at this length it leaves little room for the behavioral detail a write-to-page tool needs.

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

Completeness3/5

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

For a six-parameter page-mutating tool with no annotations and no output schema, the description covers targeting and editor detection but says nothing about failure modes, return values, or interaction with other tools in the family. Adequate, not complete.

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 the schema already documents all six parameters including clear, paste, and press_enter. The description only restates the ref-vs-selector targeting distinction and adds nothing about clear=false behavior or when paste beats the default typing path.

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

Purpose4/5

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

States a specific verb and resource ('Fill text into an input element') and names both targeting mechanisms (snapshot ref or CSS selector). It also flags special handling for contenteditable/rich text, though it never names the closest sibling browser_fill_form to make the split explicit.

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

Usage Guidelines3/5

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

Usage is only implied by the mechanics: use a ref from a snapshot or a selector. There is no statement of when to prefer this over browser_fill_form (multi-field) or browser_press_key, and no prerequisite such as needing a prior browser_snapshot to obtain '@1'.

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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