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Computer Use

by munimtechnologies
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Rust
Local

Open browser tab

browser_open_tab

Opens a URL in a background Chrome tab and returns its tab ID for follow-up browser actions like clicking, typing, or navigating. Keeps the user's browsing uninterrupted.

Instructions

Open a URL in a new background tab inside the agent's own labelled tab group in the user's signed-in Chrome, and return its tab_id for browser_snapshot, browser_click, browser_type and browser_navigate. The tab opens in the background, so the user's browsing is not interrupted. Use browser_use_tab instead when the user already has the page open and signed in. Requires the Computer Use Chrome extension; a limited fallback mode applies without it.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
urlNoAbsolute URL to open (default about:blank)
session_idNoStable task or thread ID. Pass the same value on every browser call for this task. Different IDs isolate tabs and cleanup within one MCP process. Omit for the default process session.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv0.4.3
    • addedInput schema / properties / session_id
      Added value: +{
+  "description": "Stable task or thread ID. Pass the same value on every browser call for this task. Different IDs isolate tabs and cleanup within one MCP process. Omit for the default process session.",
+  "maxLength": 128,
+  "minLength": 1,
+  "type": "string"
+}
  2. Changed1 schema field changedv0.3.1
    • changedInput schema / properties / url / description
      Previous value: -"URL to open (default about:blank)"New value: +"Absolute URL to open (default about:blank)"
  3. First observedv0.3.0

TDQS

A4.7/5.0
Behavior5/5

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

Beyond the annotations, the description discloses that the tab opens in the background, that it lives in the agent's own tab group, that it returns a tab_id for other browser tools, and that it requires the Computer Use Chrome extension with a limited fallback mode. These are material behavioral traits not present in the 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?

Three sentences, each earning its place: the core action and return value, the background behavior, and the alternative tool with extension requirement. The most important operational detail is front-loaded.

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

Completeness5/5

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

For a two-parameter optional tool with no output schema, the description is complete enough: it states what the tool returns, how the tab behaves, when to use a sibling instead, and the extension prerequisite. The agent has what it needs to invoke it correctly.

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 100%, so the schema fully documents url and session_id. The description adds context about the returned tab_id and its downstream use, but does not add parameter-level semantics beyond the schema. This matches the baseline for high schema coverage.

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 states a specific verb and resource ('Open a URL in a new background tab'), clarifies the tool's distinguishing behavior (background tab, agent's own labelled tab group), and names the return value (tab_id). This clearly differentiates it from sibling tools like browser_navigate and browser_use_tab.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description explicitly says when to use this tool: to open a URL in a new background tab without interrupting the user. It also names the alternative and the exact condition for choosing it: 'Use browser_use_tab instead when the user already has the page open and signed in.' This is direct usage guidance, not just implied.

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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