facebook-web-mcp

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Inspect live page structure (maintenance)

debug_page_structure

Read-only

Inspect the live DOM to see how many elements match given CSS selectors, with tags, attributes, and text previews, so you can fix Facebook selectors after a redesign instead of guessing.

Instructions

Report what is actually rendered on the page the browser is currently showing: how many elements match each probe selector, plus their tag, attribute names, text length and a short text preview. Use this to repair src/facebook/selectors.ts against real markup after a Facebook redesign, instead of guessing. Read-only, and it does not navigate — point the browser somewhere with a read tool first.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "debug_page_structure"
  }
}

Input Schema

Name	Required	Description
`sample`	No	How many matched elements to describe per probe
`selectors`	No	CSS selectors to probe. Defaults to the feed/post container candidates.
`show_attributes`	No	Attribute names whose VALUES to include, e.g. ["aria-label","data-ad-rendering-role"]. Attribute names alone are often not enough to tell two candidates apart.
`text_preview_chars`	No	How much text to preview per element

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Aug 1, 2026

TDQS

A4.5/5.0

Behavior5/5

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

Annotations already indicate read-only and non-destructive, but the description adds valuable behavioral detail beyond that: it does not navigate, and it enumerates the output composition (tag, attribute names, text length, preview). This gives the agent a reliable mental model of what the tool will do and return.

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?

Two sentences, front-loaded with the primary function, then use case, then a critical caveat. Every sentence carries information and there is no fluff or repetition.

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?

For a maintenance/diagnostic tool with 4 well-documented parameters, no output schema, and strong annotations, the description is sufficient. It explains what the tool reports, when to use it, and a critical constraint (does not navigate). No essential context is missing.

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% (all 4 parameters have descriptions). The tool description itself does not revisit parameter details, which is acceptable because the schema fully documents each parameter. It earns the baseline 3; no additional parameter semantics are needed.

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 uses a specific verb ('Report') and resource ('page the browser is currently showing'), and details exactly what is reported (match counts, tag, attribute names, text length, preview). It clearly distinguishes itself from siblings by framing the tool as a way to fix selector files against real markup after a redesign, rather than guessing.

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 provides a clear when-to-use context: 'Use this to repair src/facebook/selectors.ts against real markup after a Facebook redesign, instead of guessing.' It also instructs on a prerequisite ('point the browser somewhere with a read tool first') and states the tool does not navigate. However, it does not explicitly name any alternative tool or exclusion criteria, so it stops short of a full 5.

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