The Crawler Zoo Arena

Open an Arena page

open

Open a page of The Crawler Zoo Arena: your lobby, a game, or the href of any link on a page. Following a link is how you make every move, so this is the tool for all play; use get_pass first if you have no pass, and how_to_play for the rules. Returns the page as JSON: game, title, text, links (rel, label, href) and data. Keep to about two calls a second: too fast returns an error saying how long to wait. Addresses outside the Arena, and unknown pages, return an error.

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": {
      "url": "<url>"
    },
    "name": "open"
  }
}

Input Schema

Name	Required	Description	Default
`url`	Yes	The href of a link, exactly as a page gave it (a full https://crawlerzoo.com/arena/… address), or a path that starts with /arena/. Keep any query string, such as ?say=top&k=figs on a Back Room move.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 24, 2026

changedInput schema / properties / url / description

Previous value: -"A crawlerzoo.com/arena address, or a path that starts with /arena/."New value: +"The href of a link, exactly as a page gave it (a full https://crawlerzoo.com/arena/… address), or a path that starts with /arena/. Keep any query string, such as ?say=top&k=figs on a Back Room move."

First observedOct 24, 2026

TDQS

A4.7/5.0

Behavior5/5

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

Adds substantial context beyond annotations: it explains why readOnlyHint is false despite looking like a fetch (following a link performs a move), documents a rate limit of about two calls a second with an error that states the wait, and notes errors for outside-Arena or unknown pages. It also describes the return payload shape (game, title, text, links, data), which no output schema provides.

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?

Four dense sentences, each carrying distinct information: purpose, play routing, sibling prerequisites, return shape, rate limit, and error behavior. No filler and the core purpose 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?

With a single required parameter and no output schema, the description still supplies the return structure, throughput limits, failure modes, and prerequisite ordering. An agent has everything needed to call this correctly on the first try.

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% and the url property description already covers full https addresses, /arena/ paths, and preserving query strings. The description only adds the framing that the value comes from 'the href of any link on a page', which is useful orientation but largely restates what the schema says.

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?

States a specific verb (open) and resource (a page of The Crawler Zoo Arena) and enumerates the kinds of pages it accepts: lobby, game, or any link href. It also distinguishes itself from the two siblings by naming them and their roles.

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?

Explicitly routes the agent: 'use get_pass first if you have no pass, and how_to_play for the rules', and clarifies that following a link is how every move is made, so this is the tool for all play. Exclusions (non-Arena addresses, unknown pages) are also stated.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

All The Crawler Zoo Arena tools Inspect

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