Spider MCP Server

spider_browser_fill

Fill form fields by clearing existing content and typing new text, using CSS selectors for inputs, textareas, and contenteditable elements.

Instructions

Fill a form field with text. Clears existing content first, then types the new value. Use for text inputs, textareas, and contenteditable elements.

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": {
      "session_id": "<session_id>",
      "selector": "<selector>",
      "value": "<value>"
    },
    "name": "spider_browser_fill"
  }
}

Input Schema

Name	Required	Description
`value`	Yes	Text to type into the field
`timeout`	No	Max time to wait for element in ms. Default: 10000
`selector`	Yes	CSS selector of the input field (e.g. "input[name='email']", "#search-box")
`session_id`	Yes	Session ID from spider_browser_open

Schema Changelog

Changes observed during successful MCP inspections.

First observedv2.1.2Jul 6, 2026

TDQS

A4.2/5.0

Behavior4/5

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

Discloses the key behavioral trait of clearing existing content before typing, which is valuable beyond the schema. With no annotations provided, the description carries the full burden of transparency. Could add more details on handling of read-only fields or validation.

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?

Extremely concise with two short sentences: first covers purpose and behavior, second specifies supported element types. No wasted words, and the structure is front-loaded with the key action.

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

Completeness4/5

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

Given the tool's simplicity and full schema coverage, the description provides sufficient context for an agent to understand its usage. Lacks explicit mention of session requirement (though implied by session_id parameter) and return value, but no output schema exists to describe.

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 coverage is 100%, so baseline is 3. The description does not add additional semantics for parameters beyond what is already in the schema; it only describes the overall function.

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?

Clearly states the verb 'fill' and the resource 'form field', and specifies the behavior of clearing existing content before typing. Distinguishes from siblings like spider_browser_click and spider_browser_navigate by focusing on text input.

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?

Explicitly states the use case for text inputs, textareas, and contenteditable elements, providing clear context. However, it does not explicitly exclude other use cases or compare with siblings, limiting guidance on when not to use.

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