// GLOSSARY -- SECURITY & COMPLIANCE

What is Transaction Simulation?

1 min read Updated

Transaction simulation is the process of executing a blockchain transaction against the current state without actually committing it — previewing the exact outcome (token transfers, state changes, gas usage) before spending real funds.

WHY IT MATTERS

Simulation is the 'preview before publish' of blockchain transactions. Before your agent signs and submits a swap, simulation shows exactly what will happen: how many tokens you'll receive, what gas it will cost, and whether the transaction will succeed or revert.

This catches a wide range of issues: transactions that would fail (wasting gas), unexpected token movements (drainer detection), excessive slippage (bad trades), and contract interactions with unexpected side effects. For agents making autonomous decisions, simulation is a critical safety check.

Services like Tenderly, Blowfish, and Alchemy provide simulation APIs. The agent constructs a transaction, calls the simulation API, analyzes the simulated outcome, and only signs if the result matches expectations.

HOW POLICYLAYER USES THIS

PolicyLayer can integrate transaction simulation as part of policy validation. Before approving an agent transaction, simulate it to verify the outcome matches expectations — catching issues that policy rules alone might miss.

FREQUENTLY ASKED QUESTIONS

How accurate is transaction simulation?
Very accurate for the current state. However, state can change between simulation and execution (MEV, other transactions). For time-sensitive DeFi, simulate close to execution time and include slippage tolerance.
Which simulation services are available?
Tenderly (most comprehensive), Blowfish (security-focused), Alchemy (integrated with their node service), and native eth_call (basic simulation available on any RPC node).
Should every agent transaction be simulated?
For high-value or complex transactions, yes. For simple stablecoin transfers to known addresses, simulation adds latency without much benefit. Use simulation based on transaction risk profile.

FURTHER READING

Enforce policies on every tool call

Intercept is the open-source MCP proxy that enforces YAML policies on AI agent tool calls. No code changes needed.

npx -y @policylayer/intercept
github.com/policylayer/intercept →
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