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ZERO Payment Guard

by host.beacon.worker.zero-payment-guard
OverviewDiscussionsAdmin

Web page to Markdown + metadata ($0.001 USDC on Base via x402)

page_extract
Read-onlyIdempotent

Paid $0.001 per call (x402, USDC on Base). Fetch a public web page and return its main content as clean Markdown plus metadata: title, description, canonical, language, author, dates, OpenGraph/Twitter card, JSON-LD types, headings outline, favicon, feeds, link counts (links=true for the list). Honours robots.txt.

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": {
      "url": "<url>"
    },
    "name": "page_extract"
  }
}

Input Schema

NameRequiredDescriptionDefault
urlYesPublic http(s) URL
linksNoInclude up to 150 links
maxCharsNoMax Markdown chars, default 20000

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observed

TDQS

A3.7/5.0
Behavior4/5

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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the bar is lower, yet the description still adds real context: a per-call cost of $0.001 in USDC on Base via x402, robots.txt compliance, and the exact shape of the returned metadata (link counts, JSON-LD types, headings outline). It stops short of covering failure/refund behavior or rate limits.

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 dense sentences, front-loaded with the payment constraint before the fetch behavior. The metadata enumeration is long but each item earns its place by telling the agent what it will receive.

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?

With no output schema, the description carries the burden of describing returns and does so thoroughly (title, canonical, OG/Twitter, JSON-LD, outlines, feeds, links). For a paid, read-only fetch tool the remaining unknown is the payment handshake, which is delegated to siblings but never named.

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 url, links and maxChars with formats and bounds. The description only reinforces the links parameter ("links=true for the list"), adding marginal meaning beyond the schema — the baseline 3 is appropriate.

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?

"Fetch a public web page and return its main content as clean Markdown plus metadata" states a specific verb and resource, and the enumeration of metadata fields makes the output concrete. It does not, however, say anything that separates it from page_extract_batch (single page vs. many), so sibling differentiation is left to the agent.

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 implied rather than stated: the price line signals this is a paid call on public URLs and "Honours robots.txt" hints at acceptable targets. There is no explicit when-to-use / when-not-to-use rule and no pointer to x402_preflight or usdc_payment_check for the payment flow.

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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