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umbra

umbra

by lxchx
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Remote

Navigate

navigate

Loads a URL in an existing tab while preserving stealth payload and cookies; set timeout_s to cap load time.

Instructions

Navigate tab. Stealth payload + cookies persist. Cheaper than spawn — default reflex.

timeout_s: hard cap on load (default 30s). Raises on timeout (tab survives, retry/abort). Ex: navigate('t0', 'https://example.com/login') → {"url":"..."}

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": {
      "tab_id": "<tab_id>",
      "url": "<url>"
    },
    "name": "navigate"
  }
}

Input Schema

NameRequiredDescriptionDefault
urlYes
tab_idYes
timeout_sNo

Output Schema

NameRequiredDescriptionDefault

No arguments

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A4/5.0
Behavior4/5

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

With no annotations available, the description carries the behavioral burden and does well: it discloses stealth payload persistence, cookie persistence, the default timeout, and that timeout raises while the tab survives for retry or abort. It does not cover all possible side effects, but it gives substantial beyond-schema behavior.

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 short and front-loaded: purpose, persistence behavior, default status, timeout behavior, and an example. Every line adds concrete information and there is no wasted prose.

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?

Given the lack of annotations and the presence of an output schema, the description is mostly complete: it explains loading behavior, persistence, and timeout failure handling. The main omission is that tab_id's source or relationship to list_tabs is not stated, which could matter for correct invocation.

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 0%, so the description must compensate. It explains timeout_s well and gives an example showing tab_id and url, but it does not define what tab_id means or where to get one, leaving required-parameter semantics only partially covered.

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 and resource: 'Navigate tab' with a URL target shown in the example. It also differentiates from the sibling 'spawn' by calling itself cheaper and the default reflex, though it does not distinguish navigation from siblings such as reload, back, or forward.

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

Usage Guidelines4/5

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

It explicitly recommends this as the default and says it is cheaper than spawn, giving clear guidance on when to prefer it over that alternative. It lacks exclusions for other navigation-related siblings, but the intended default usage is clear.

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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