Evaluates a proposed transaction against a caller-supplied set of risk rules before signing, returning a per-rule pass/fail/skip breakdown and an overall approved verdict. Rules are caller-defined — Syenite does not impose or modify them. Supported rules: maxValueNative (cap native token value), ...
Risk signalsHigh parameter count (15 properties)
Part of the Syenite server.
Free to start. No card required.
AI agents use tx.guard to create or modify resources in Syenite. Write operations carry medium risk because an autonomous agent could trigger bulk unintended modifications. Rate limits prevent a single agent session from making hundreds of changes in rapid succession. Argument validation ensures the agent passes expected values.
Without a policy, an AI agent could call tx.guard repeatedly, creating or modifying resources faster than any human could review. PolicyLayer's rate limiting ensures write operations happen at a controlled pace, and argument validation catches malformed or unexpected inputs before they reach Syenite.
Write tools can modify data. A rate limit prevents runaway bulk operations from AI agents.
{
"version": "1",
"default": "deny",
"tools": {
"tx.guard": {
"limits": [
{
"counter": "tx.guard_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}See the full Syenite policy for all 46 tools.
These attack patterns abuse exactly the kind of access tx.guard gives an agent. Each links to the full case and the policy that stops it:
Other write tools across the catalogue. The same approach applies to each: rate-limit and validate the arguments.
Evaluates a proposed transaction against a caller-supplied set of risk rules before signing, returning a per-rule pass/fail/skip breakdown and an overall approved verdict. Rules are caller-defined — Syenite does not impose or modify them. Supported rules: maxValueNative (cap native token value), allowedContracts (allowlist of target addresses), blockedContracts (denylist), allowedFunctions (function selector filter), requireVerifiedContract (flag if contract is unverified — requires prior tx.verify call), requireAllowlisted (flag if contract is not in Syenite's curated protocol registry), and maxGasLimit. Pass transaction (to, data, value, gasLimit, chainId) and rules (any subset of the above); at least one rule is required. Use as a programmable safety gate before any autonomous on-chain action. Does not submit or sign the transaction.. It is categorised as a Write tool in the Syenite MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Syenite MCP server in PolicyLayer and add a rule for tx.guard: 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 Syenite. Nothing to install.
tx.guard is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the tx.guard 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 tx.guard. 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.
tx.guard is provided by the Syenite MCP server (@syenite/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 46 Syenite tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
4,600+ MCP servers and 31,000+ tools scanned and risk-classified.