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Novarithm Agent Hub: trust and commerce checks

by com.novarithm.www
OverviewDiscussionsAdmin

web_screenshot

[PAID $0.03 USDC/call, x402, eip155:8453] Capture any public page as a PNG through a headless browser and return it base64-encoded, with its exact dimensions. For agents that must see a page, archive a price display or prove what a site showed at a given instant.

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": "web_screenshot"
  }
}

Input Schema

NameRequiredDescriptionDefault
hNoViewport height in pixels (default 800)
wNoViewport width in pixels (default 1280)
urlYesFull http(s) URL

Schema Changelog

Changes observed during successful MCP inspections.

  1. Added

TDQS

A3.6/5.0
Behavior3/5

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

With no annotations, the description carries the full burden and does well on cost/auth context: it discloses the $0.03 USDC per-call charge, the x402 payment scheme and chain, and that only public pages are reachable. It omits operational behavior an agent needs — render timeouts, JS wait strategy, failure/refund behavior, payload size limits, or whether the capture is viewport-only.

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 pricing/payment metadata an agent must decide on first, then the operation, then the motivating use cases. No filler or repetition.

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 correctly fills the gap by stating the return is a base64-encoded PNG with exact dimensions. For a three-parameter read tool this is nearly enough, though failure modes and capture scope (viewport vs full page) remain unstated.

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 url, w and h (with defaults) are already documented in the schema. The description adds only the notion of "exact dimensions" returned, and never mentions the viewport width/height inputs or what values they accept, so it adds little beyond the schema.

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 ("Capture any public page as a PNG through a headless browser") plus output encoding and dimensions. It does not distinguish itself from near-siblings like web_render, web_fetch or web_status, so an agent must infer the difference from the name alone.

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?

Gives use cases ("agents that must see a page, archive a price display or prove what a site showed at a given instant") which is genuine context. However it never says when NOT to use it or names an alternative such as web_fetch for text-only extraction, which matters given several overlapping web tools.

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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