Sign an EVM transaction. Two actions: (1) sign-unsigned-hex: sign pre-built unsigned tx hex; (2) sign-from-details: build and sign from fields (blockchain, network, toAddress, value, gas, fee, etc.). Network names (e.g. ethereum+sepolia, polygon+mainnet) are mapped to chainId internally. Private ...
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AI agents invoke evm_sign to trigger processes or run actions in Mcp Signer. Execute operations can have side effects beyond the immediate call -- triggering builds, sending notifications, or starting workflows. Rate limits and argument validation are essential to prevent runaway execution.
evm_sign can trigger processes with real-world consequences. An uncontrolled agent might start dozens of builds, send mass notifications, or kick off expensive compute jobs. PolicyLayer enforces rate limits and validates arguments to keep execution within safe bounds.
Execute tools trigger processes. Rate-limit and validate arguments to prevent unintended side effects.
{
"version": "1",
"default": "deny",
"tools": {
"evm_sign": {
"limits": [
{
"counter": "evm_sign_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}See the full Mcp Signer policy for all 4 tools.
These attack patterns abuse exactly the kind of access evm_sign gives an agent. Each links to the full case and the policy that stops it:
Other execute tools across the catalogue. The same approach applies to each: rate-limit and validate the arguments.
Sign an EVM transaction. Two actions: (1) sign-unsigned-hex: sign pre-built unsigned tx hex; (2) sign-from-details: build and sign from fields (blockchain, network, toAddress, value, gas, fee, etc.). Network names (e.g. ethereum+sepolia, polygon+mainnet) are mapped to chainId internally. Private key is always passed as parameter (never from env). SECURITY: Private keys may be logged by MCP clients or stored in conversation history — use only in trusted local environments.. It is categorised as a Execute tool in the Mcp Signer MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Mcp Signer MCP server in PolicyLayer and add a rule for evm_sign: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Mcp Signer. Nothing to install.
evm_sign is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the evm_sign rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for evm_sign. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
evm_sign is provided by the Mcp Signer MCP server (@cryptoapis-io/mcp-signer). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 4 Mcp Signer tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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