Once vs Simma

In-depth architectural comparison of the Once and Simma MCP servers. Compare execution transports, security boundaries, tool capabilities, quality scores, and ready-to-paste client installation snippets for Claude, Cursor, Windsurf, and VS Code.

Which MCP Server Should You Choose?

Choose Once when:

• You need dedicated capabilities in the Developer Tools domain.
• You prefer local stdio subprocess transport architecture.
• Your security boundary fits: No auth required (Free / Open Source).

Explore Once Details

S

Choose Simma when:

• You need dedicated capabilities in the Developer Tools domain.
• You prefer local stdio subprocess transport architecture.
• Your security boundary fits: No auth required (Free / Open Source).

Explore Simma Details

Feature & Specification Comparison

Specification	Once Developer Tools	S Simma Developer Tools
Summary	Run a side effect exactly once under retries, redelivery, and concurrent workers.	Your swim, run and ride training, explained. For coaches and athletes, computed from Garmin data.
Category & Scope	Developer Tools	Developer Tools
Quality signal

Tools & Capabilities Breakdown

Ready-to-Paste Client Configurations

Paste either (or both) of these JSON server blocks into your client config file (e.g. claude_desktop_config.json or ~/.cursor/mcp.json).

{
  "mcpServers": {
    "once": {
      "command": "uvx",
      "args": [
        "once-kernel"
      ]
    }
  }
}

{
  "mcpServers": {
    "simma": {
      "command": "npx",
      "args": [
        "-y",
        "simma"
      ]
    }
  }
}

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