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Mochi

Mochi

by DevZonayed
OverviewSchemaSourceRelated ServersDiscussionsAdmin
JavaScript
Local

browser_screenshot

Take PNG or JPEG screenshots of browser tabs (viewport, fullPage, elementRef) even when the tab is in the background. Supports automated web testing and visual verification.

Instructions

PNG/JPEG screenshot of the session tab (CDP-based; works whether the tab is foreground or background). Modes: viewport (default), fullPage, elementRef.

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": "browser_screenshot"
  }
}

Input Schema

NameRequiredDescriptionDefault
fullPageNo
elementRefNo
formatNopng
tabIdNo

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

B3.1/5.0
Behavior3/5

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

No annotations exist, so the description carries the burden. It reveals that the screenshot works even if the tab is in the background and that it uses CDP. However, it does not disclose if the operation is read-only, any side effects, authorization needs, or rate limits, which is a gap for a tool with no annotations.

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 cover the core purpose and modes. No fluff, front-loaded with the main action. Very efficient.

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?

The tool has no output schema and 4 parameters. The description ignores the format and tabId parameters and does not mention what the return value is (e.g., base64 image). Completeness is adequate for a simple tool but gaps remain in parameter coverage and result format.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters2/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

With 0% schema description coverage, the description adds meaning for fullPage and elementRef by naming them as modes (viewport, fullPage, elementRef). But it fails to mention the format parameter (png/jpeg) or tabId (which tab to screenshot), leaving half the parameters unexplained.

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?

The description clearly states the tool takes a PNG/JPEG screenshot of the session tab, which is a specific verb and resource. It mentions CDP-based and works in background, but does not explicitly distinguish from sibling DOM capture tools like browser_snapshot, though the difference is implied.

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?

No guidance on when to use this tool versus alternatives like browser_snapshot or browser_emulate_viewport. The description lists modes but does not explain when to choose each mode, leaving the agent without usage context.

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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