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zen-browser

zen-browser

by grapedjuice
OverviewSchemaSourceRelated ServersDiscussionsAdmin
JavaScript
Local

read_page

Reads a browser page as an accessibility-style tree and tags interactive elements with [ref_N], enabling accurate targeting for clicks and form inputs.

Instructions

Read the page as an accessibility-style tree. Interactive elements are tagged [ref_N] for use with computer/form_input.

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": "read_page"
  }
}

Input Schema

NameRequiredDescriptionDefault
tabIdNoTab to act on. Defaults to the active tab of the focused Zen window.
filterNo'interactive' lists only clickable/typable elements.
ref_idNoOnly return the subtree under this ref.
max_charsNo

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv1.0.0

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; it does disclose the output shape (accessibility tree with ref tags) and the downstream contract with computer/form_input. It omits truncation behavior, whether the page is scrolled or fully traversed, default tab resolution, and any side effects — meaningful gaps for a read tool with no structured hints.

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 output format, with zero filler. The second sentence earns its place by explaining the ref convention and its consumers.

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?

For a 4-parameter read tool with no output schema, the description conveys enough about the return value (tree structure, ref tags) and workflow linkage to call it correctly. The main residual gap is truncation and max_chars behavior, which is minor relative to the rest.

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 coverage is 75%, so the schema already documents tabId, filter, and ref_id. The description's explanation of [ref_N] tagging indirectly clarifies the ref_id parameter, adding marginal meaning, but max_chars remains undocumented in both places and no format or size guidance is given.

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 — read the page — and characterizes the output form as an 'accessibility-style tree' with [ref_N] tagged interactive elements, which distinguishes it from siblings like get_page_text and screenshot. It does not explicitly name those siblings, so a 4 rather than a 5.

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 mention that refs are for use with computer/form_input implies the read->act workflow, which is useful context. However, there is no explicit statement of when to choose this over get_page_text, screenshot, or find, nor any exclusion guidance.

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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