Call state-changing contract functions. Auto-fetches ABI. DRY_RUN default — pass confirm='CONFIRMED' to execute. Requires EVM_PRIVATE_KEY.
Risk signalsHigh parameter count (12 properties)
Part of the Kosyak Evm server.
Free to start. No card required.
AI agents use write_contract to create or modify resources in Kosyak Evm. 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 write_contract 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 Kosyak Evm.
Write tools can modify data. A rate limit prevents runaway bulk operations from AI agents.
{
"version": "1",
"default": "deny",
"tools": {
"write_contract": {
"limits": [
{
"counter": "write_contract_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}See the full Kosyak Evm policy for all 50 tools.
These attack patterns abuse exactly the kind of access write_contract 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.
Call state-changing contract functions. Auto-fetches ABI. DRY_RUN default — pass confirm='CONFIRMED' to execute. Requires EVM_PRIVATE_KEY.. It is categorised as a Write tool in the Kosyak Evm MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Kosyak Evm MCP server in PolicyLayer and add a rule for write_contract: 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 Kosyak Evm. Nothing to install.
write_contract 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 write_contract 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 write_contract. 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.
write_contract is provided by the Kosyak Evm MCP server (kosyak-evm-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 50 Kosyak Evm 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.