Start the public Posterly paid signup flow for a user before Posterly API access exists. Returns a Posterly checkout handoff URL and signup poll URL. The user must handle payment and password setup in the browser. Do not ask for card details or a Posterly password in chat.
AI agents use start_signup to commit financial operations through Posterly — usually the final step of a payment, billing, or trading workflow. A call moves real money.
This tool initiates a paid signup/checkout flow, which commits the user to a financial obligation (subscription or purchase). Even though payment is handled in the browser, the tool directly triggers the financial transaction process, placing it in the Financial category with high severity due to potential for unwanted charges.
From the tool's definition 'Start the public Posterly paid signup flow', 'Returns a Posterly checkout handoff URL', 'The user must handle payment and password setup in the browser'
Attacks that exploit this kind of access
Start the public Posterly paid signup flow for a user before Posterly API access exists. Returns a Posterly checkout handoff URL and signup poll URL. The user must handle payment and password setup in the browser. Do not ask for card details or a Posterly password in chat. It is categorised as a Financial tool in the Posterly MCP Server, which means it involves financial transactions. Block by default and require explicit approval.
Register the Posterly MCP server in PolicyLayer and add a rule for start_signup: 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 Posterly. Nothing to install.
start_signup is a Financial tool with critical risk. Critical-risk tools should be blocked by default and only enabled with explicit human approval.
Yes. Add a rate_limit block to the start_signup 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 start_signup. 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.
start_signup is provided by the Posterly MCP server (posterly-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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