Create a webhook subscription that pushes grant-change events matching a filter. Cost: $0.20 USDC via x402 (paid by the agent runtime). On 402 response, agent must satisfy payment and retry.
Risk signalsAccepts URL/endpoint input (callback_url)
Part of the Mcp Server server.
Free to start. No card required.
AI agents use subscribe_changes to create or modify resources in Mcp Server. 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 subscribe_changes 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 Mcp Server.
Write tools can modify data. A rate limit prevents runaway bulk operations from AI agents.
{
"version": "1",
"default": "deny",
"tools": {
"subscribe_changes": {
"limits": [
{
"counter": "subscribe_changes_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}See the full Mcp Server policy for all 8 tools.
These attack patterns abuse exactly the kind of access subscribe_changes 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.
Create a webhook subscription that pushes grant-change events matching a filter. Cost: $0.20 USDC via x402 (paid by the agent runtime). On 402 response, agent must satisfy payment and retry.. It is categorised as a Write tool in the Mcp Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Mcp Server MCP server in PolicyLayer and add a rule for subscribe_changes: 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 Server. Nothing to install.
subscribe_changes 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 subscribe_changes 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 subscribe_changes. 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.
subscribe_changes is provided by the Mcp Server MCP server (@localgov-jp/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 8 Mcp Server tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
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