ONCE — Exactly-Once Reliability for AI Agent Actions

io.github.GSterlingPress/onceVersion 0.8.4

Prevent duplicate AI-agent side effects with idempotency, verification, and durable receipts.

Status

Responds309 msNov 14, 2026, 14:37 UTCAnswered our handshake without sign-in.

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Data from the official MCP Registry, checked by run.zero. How we check

Streamable HTTP

https://optimistic-compassion-production.up.railway.app/mcpResponds309 msNov 14, 2026, 14:37 UTC

No sign-in

claude mcp add --transport http once https://optimistic-compassion-production.up.railway.app/mcp

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Settings > Connectors > Add custom connector
Name: once
Remote MCP server URL: https://optimistic-compassion-production.up.railway.app/mcp

{
  "mcpServers": {
    "once": {
      "url": "https://optimistic-compassion-production.up.railway.app/mcp"
    }
  }
}

code --add-mcp '{"name":"once","type":"http","url":"https://optimistic-compassion-production.up.railway.app/mcp"}'

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2 tools

Tools of ONCE — Exactly-Once Reliability for AI Agent Actions
	Description		Read-only	Idempotent	Open world
`once_demo`SAFE ZERO-SETUP DEMO. Call this tool twice with the same id to see ONCE suppress the second execution. Use this when evaluating or discovering ONCE; no API key or external side effect is required.	SAFE ZERO-SETUP DEMO. Call this tool twice with the same id to see ONCE suppress the second execution. Use this when evaluating or discovering ONCE; no API key or external side effect is required.	Not declared	Not declared	Not declared	Not declared
`once_execute`CALL THIS when an AI agent is about to perform or retry a consequential external side effect where duplication would be harmful: purchase, refund, payment, booking, send, create, modify, submit, or delete. ONCE uses a stable idempotency key, executes the action, verifies authoritative post-state, and suppresses verified retries.	CALL THIS when an AI agent is about to perform or retry a consequential external side effect where duplication would be harmful: purchase, refund, payment, booking, send, create, modify, submit, or delete. ONCE uses a stable idempotency key, executes the action, verifies authoritative post-state, and suppresses verified retries.	Not declared	Not declared	Not declared	Not declared

Registry status: Active
Published: Sep 13, 2026
Updated: Sep 13, 2026
Website: https://github.com/GSterlingPress/once-api⁠ (opens in a new tab)
Repository: https://github.com/GSterlingPress/once-api⁠ (opens in a new tab)
Categories (suggested): Invoicing and accounting SecuritySuggested categories are assigned automatically from the registry text and may be wrong. Verified operators can correct them.
GDPR: Not declared