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Xzar

Official registry AI and agents

Crash-test your AI agent on real professional decisions, graded against what actually happened.

Source code Website Documentation

Install

Add this to your client's MCP configuration (Claude Desktop: claude_desktop_config.json; Cursor: .cursor/mcp.json; VS Code and others use the same "mcpServers" shape).

Remote (streamable-http)
Claude Code 
claude mcp add --transport http xzar 'https://api.xzar.si/mcp'
JSON configuration (Claude Desktop, Cursor, VS Code) 
{
    "mcpServers": {
        "xzar": {
            "type": "http",
            "url": "https://api.xzar.si/mcp"
        }
    }
}
PYPI package xzar-mcp
Claude Code 
claude mcp add xzar -e 'XZAR_API_KEY=<your xzar_api_key>' -e 'XZAR_API_URL=<XZAR_API_URL>' -- uvx xzar-mcp==0.1.2
JSON configuration (Claude Desktop, Cursor, VS Code) 
{
    "mcpServers": {
        "xzar": {
            "command": "uvx",
            "args": [
                "xzar-mcp==0.1.2"
            ],
            "env": {
                "XZAR_API_KEY": "<your xzar_api_key>",
                "XZAR_API_URL": "<XZAR_API_URL>"
            }
        }
    }
}

Environment variables

  • XZAR_API_KEY required secret Your Xzar API key (https://xzar.si/signup.html)
  • XZAR_API_URL Override the API base URL (default https://api.xzar.si); for local development only

Documentation

From the project's README on GitHub, refreshed weekly. Links open on GitHub.

Contents
  1. Xzar MCP server
  2. Setup
  3. Hosted connector (no install)
  4. Claude plugin
  5. Tools
  6. Pricing

Xzar MCP server

Crash-test your AI agent on real professional decisions. Xzar gives your agent real cases, cut at the moment of decision, and grades its answer against what the professional actually decided. Most cases were decided after current models were trained, so they can't have been memorized; fresh ones are added monthly.

Live today:

  • Tariff classification: real U.S. classification decisions, graded exactly at 2, 4, 6, 8 and 10 digits, with a consistency check (the same case asked twice). Testing a tariff classifier? See https://xzar.si/scorecard
  • Patent examination: first action, response and appeal.

More fields are on the way; ask for yours at https://xzar.si.

Setup

  1. Get an API key (with $5 of free credit) at https://xzar.si/signup.html
  2. Add the server to your MCP client:
{
  "mcpServers": {
    "xzar": {
      "command": "uvx",
      "args": ["xzar-mcp"],
      "env": { "XZAR_API_KEY": "your-key" }
    }
  }
}

Hosted connector (no install)

In Claude or any MCP client that supports remote servers: add https://api.xzar.si/mcp and sign in with your Xzar API key.

Claude plugin

The plugin/ folder is the Xzar plugin for Claude. It bundles the hosted connector with two skills: crash-test, which runs a task end to end and explains the score, and xzar-request, for custom tests, pilots, quotes and training access. In Claude Code:

/plugin install xzar --marketplace xzar-si/xzar-mcp

Tools

ToolWhat it does
start_taskStart a task: the case, the instructions and the tool budget
search_librarySearch the case's reference library
read_publicationRead one library item
search_rulesSearch the professional rulebook for the task
read_ruleRead one rulebook section
submit_answerSubmit the decision; returns the exact score and the grade receipt
request_serviceAsk for a custom test for your field, a pilot, a quote, or training access; get a reference and next steps
get_scorecardYour agent's scorecard across tasks
get_usageCredit balance and usage

Answer keys never leave Xzar's servers. This package holds no tasks; it calls the Xzar API with your key.

Pricing

Prepaid credits, charged per task. See https://xzar.si/docs.html. Pilots and ongoing testing: https://xzar.si.

Frequently asked questions

What is Xzar?

Crash-test your AI agent on real professional decisions, graded against what actually happened.

How do I install Xzar?

It runs as a remote server. In Claude Code: claude mcp add --transport http xzar 'https://api.xzar.si/mcp'. For other clients, paste the JSON configuration from this page into their MCP settings.

Does Xzar need an API key?

Yes. It expects XZAR_API_KEY, which you set in its configuration.

Is Xzar open source?

Yes. Its code is on GitHub under the MIT license.

Who maintains Xzar?

It is published by xzar-si. AI.tn lists it but does not maintain or endorse it.

From the official MCP Registry. Listing is not an endorsement: review a server's code and permissions before giving it access to your data.