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zen-browser

zen-browser

by grapedjuice
OverviewSchemaSourceRelated ServersDiscussionsAdmin
JavaScript
Local

screenshot

Captures the visible area of a browser tab as an image, bringing that tab to the front first so the current view is recorded.

Instructions

Capture the visible part of a tab as an image. The tab is brought to the front 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": "screenshot"
  }
}

Input Schema

NameRequiredDescriptionDefault
tabIdNoTab to act on. Defaults to the active tab of the focused Zen window.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv1.0.0

TDQS

B3.3/5.0
Behavior3/5

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 does disclose one important side effect — the tab is brought to the front first — which an agent would not otherwise know. It does not state what the image is returned as (inline data vs. file path), whether lazy-loaded content is included, or any permission or rate constraints.

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 short sentences, front-loaded with the core action and followed by the one non-obvious behavior. No redundant or filler wording.

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?

For a one-optional-parameter tool with a fully documented schema and no output schema, the definition is minimally sufficient. The main gap is the return value: an agent cannot tell whether it receives image data it can interpret or a reference it must handle differently.

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%, and the tabId description already explains the default (active tab of the focused Zen window). The tool description adds nothing about the parameter beyond that, which is acceptable at full coverage but not value-adding.

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 states a specific verb ("Capture") and a specific resource/scope ("the visible part of a tab as an image"), which is unambiguous. It does not differentiate itself from plausible siblings such as read_page, get_page_text, or computer, which could also be used to observe a page.

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?

There is no explicit guidance on when to use this instead of read_page, get_page_text, computer, or javascript for inspecting a page. The implied usage (visual capture) is inferable from the name and first sentence, but no alternatives or exclusions are named.

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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