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pipethedev
by pipethedev

browsercat_fill

Automatically populate web form fields using CSS selectors to input specified values, enabling automated data entry in browser interactions.

Instructions

Fill out an input field

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
selectorYesCSS selector for input field
valueYesValue to fill

Implementation Reference

  • The handler for the 'browsercat_fill' tool. It waits for the specified selector to appear, types the provided value into the input field using Puppeteer's page.type method, and returns success or error message.
    case "browsercat_fill":
      try {
        await page.waitForSelector(args.selector);
        await page.type(args.selector, args.value);
        return {
          content: [{
            type: "text",
            text: `Filled ${args.selector} with: ${args.value}`,
          }],
          isError: false,
        };
      } catch (error) {
        return {
          content: [{
            type: "text",
            text: `Failed to fill ${args.selector}: ${(error as Error).message}`,
          }],
          isError: true,
        };
      }
  • Tool definition including name, description, and input schema for 'browsercat_fill'. Defines required parameters: selector (CSS selector for input) and value (string to fill).
    {
      name: "browsercat_fill",
      description: "Fill out an input field",
      inputSchema: {
        type: "object",
        properties: {
          selector: { type: "string", description: "CSS selector for input field" },
          value: { type: "string", description: "Value to fill" },
        },
        required: ["selector", "value"],
      },
    },
  • index.ts:421-423 (registration)
    Registration of all tools (including browsercat_fill) via the ListToolsRequestSchema handler, which returns the TOOLS array containing the tool definitions.
    server.setRequestHandler(ListToolsRequestSchema, async () => ({
      tools: TOOLS,
    }));
  • index.ts:425-427 (registration)
    Registration of the CallToolRequestSchema handler, which dispatches tool calls (including browsercat_fill) to the handleToolCall function based on the tool name.
    server.setRequestHandler(CallToolRequestSchema, async (request) =>
      handleToolCall(request.params.name, request.params.arguments ?? {})
    );
Behavior2/5

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It states the action ('fill out') but doesn't describe what happens after filling (e.g., does it trigger events, is it idempotent, are there side effects like form submission). For a mutation tool with zero annotation coverage, this is a significant gap in transparency about behavior beyond the basic action.

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?

The description is a single, efficient sentence ('Fill out an input field') that directly states the purpose without unnecessary words. It is appropriately sized for a simple tool, though it could be more front-loaded with context if needed. There is no waste, but it might be too brief for optimal clarity.

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 the tool's complexity (a mutation operation with no annotations and no output schema), the description is incomplete. It doesn't cover behavioral aspects like error handling, what the tool returns, or how it interacts with the browser context. For a tool that modifies state, more context is needed to ensure safe and correct usage by an AI agent.

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?

The input schema has 100% description coverage, with clear documentation for both parameters ('selector' as CSS selector and 'value' as value to fill). The description adds no additional meaning beyond what the schema provides, such as examples or constraints. With high schema coverage, the baseline is 3, as the schema does the heavy lifting for parameter semantics.

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

Purpose3/5

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

The description 'Fill out an input field' clearly states the action (fill) and target (input field), making the basic purpose understandable. However, it lacks specificity about what type of input fields or context (e.g., web forms, UI automation) and doesn't distinguish from sibling tools like 'browsercat_click' or 'browsercat_select' which might also interact with input fields. The description is functional but vague about scope.

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?

The description provides no guidance on when to use this tool versus alternatives. It doesn't mention sibling tools like 'browsercat_click' (for clicking) or 'browsercat_select' (for selecting options), leaving the agent to infer usage based on the name alone. There are no explicit when/when-not instructions or prerequisites, such as requiring a page to be loaded first.

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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