EffectFence MCP server

EffectFence is a small helper that sits between your AI agents and the tools they use, so the same action never runs twice by accident. It is handy if you have several agents (or retries) that might all try to charge a card, send a payout, or change a server at the same time. Think of it as a traffic cop for dangerous actions.

What this MCP server does

You (or your agents) ask your AI to do something risky, like charge order 123. Your AI sends that request to EffectFence instead of running it directly. EffectFence checks if the same action already ran, is running right now, or if the information behind the decision is out of date. If it is safe, exactly one attempt goes through and gets a sealed receipt. Every other duplicate gets that same receipt replayed, or is told to stand down, so nothing runs twice.

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What you can do with it

• Prevent the same charge from firing twice when two agents race
• Replay the original result to late duplicates instead of running again
• Refuse an action if the data it was based on has changed
• Let exactly one agent act when several disagree about the same resource
• Record a sealed receipt for every action that actually ran
• Probe your own tool server to see if it double-fires
• Wrap an existing MCP tool server so every call is fenced automatically

Try asking your AI

• “Charge order 123 for $49, but make sure it only happens once”
• “Two agents want to scale the same server in opposite directions. Let only one act.”
• “Check if my payment tool server double-charges when called twice at the same time”
• “Wrap my existing tool server so duplicate calls are replayed instead of re-run”

What it gives back to you

You get a clear answer in the chat: either the action ran and you see the recorded result, or you are told it was already done and given the earlier result, or you are told it was refused and why. If you run a probe, you get a short report showing how many distinct effects actually landed. If you wrap a server, every tool call flows through and you see the normal results, just without duplicates.

Before you start

Who it's for

Developers and teams running AI agents that move money, change servers, or take any action that must not happen twice.