Construct, sign, and send a transaction
AI agents invoke send_dynamic_signed_transaction to trigger actions in Substrate MCP Server. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.
This tool signs and submits blockchain transactions, which triggers irreversible on-chain state changes. It can transfer tokens, invoke smart contracts, or call any pallet extrinsic. While some transactions might be considered Financial, the general-purpose nature covers arbitrary execution. The blast radius is critical since a misused tool could drain funds, alter governance, or permanently modify chain state.
From the tool's definition Construct, sign, and send a transaction
Documented attack patterns abuse exactly the kind of access send_dynamic_signed_transaction gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Substrate MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for send_dynamic_signed_transaction:
{
"version": "1",
"default": "deny",
"tools": {
"send_dynamic_signed_transaction": {
"limits": [
{
"counter": "send_dynamic_signed_transaction_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}send_dynamic_signed_transaction stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.
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Construct, sign, and send a transaction. It is categorised as a Execute tool in the Substrate MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Substrate MCP Server MCP server in PolicyLayer and add a rule for send_dynamic_signed_transaction: 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 Substrate MCP Server. Nothing to install.
send_dynamic_signed_transaction 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 send_dynamic_signed_transaction 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 send_dynamic_signed_transaction. 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.
send_dynamic_signed_transaction is provided by the Substrate MCP Server MCP server (thomasmarches/substrate-mcp-rs). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Substrate MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
13 Substrate MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.