Riddle MCP Server

riddle_screenshot

Capture screenshots of web pages across desktop, tablet, and mobile devices using the Riddle API. Returns base64-encoded PNG images for documentation, testing, or visual verification.

Instructions

Take a screenshot of a URL using the Riddle API. Returns base64-encoded PNG image.

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": "riddle_screenshot"
  }
}

Input Schema

Name	Required	Description
`url`	Yes	URL to screenshot
`width`	No	Viewport width (default: 1280)
`height`	No	Viewport height (default: 720)
`device`	No	Device preset (overrides width/height)

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Jan 7, 2026

TDQS

A3.5/5.0

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. It mentions the API ('Riddle API') and output format, but lacks details on behavioral traits such as rate limits, authentication needs, error handling, or whether the operation is idempotent. For a tool with no annotation coverage, this is a significant gap in transparency.

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?

The description is a single, efficient sentence that front-loads the core action ('Take a screenshot') and includes essential details (resource, API, output format) without unnecessary words. Every part of the sentence adds value, making it highly concise and well-structured.

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

Completeness3/5

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

Given no annotations and no output schema, the description provides basic purpose and output format but lacks completeness for a tool with 4 parameters and potential complexity (e.g., API behavior, error cases). It is adequate as a minimum viable description but has clear gaps in contextual details needed for full understanding.

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 all parameters (url, width, height, device) with descriptions and defaults. The description does not add any parameter-specific semantics beyond what the schema provides, such as explaining interactions between device and width/height, so it meets the baseline of 3.

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 clearly states the specific action ('Take a screenshot') and resource ('of a URL using the Riddle API'), distinguishing it from siblings like 'riddle_batch_screenshot' (multiple screenshots) and 'riddle_click_and_screenshot' (interactive screenshot). It explicitly mentions the output format ('base64-encoded PNG image'), which helps differentiate its purpose.

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?

The description implies usage for single URL screenshots but does not explicitly state when to use this tool versus alternatives like 'riddle_batch_screenshot' for multiple URLs or 'riddle_click_and_screenshot' for interactive actions. No exclusions or prerequisites are mentioned, leaving usage context somewhat vague.

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

Deploy Server