AI agents call check_balance to retrieve information from Z Zero without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
| Parameter | Type | Required | Description |
|---|---|---|---|
card_alias | string | Yes | The alias of the card to check, e.g. 'Card_01' |
Parameters from the server's own tool schema.
The tool retrieves financial information (account balance) but does not move money, execute transactions, or modify any state. It is analogous to checking an account balance, which is a read-only operation. While it operates in a financial domain, the actual capability is purely informational. Severity is low because misuse would only expose data, not commit financial obligations or cause irreversible harm.
From the tool's definition Tool description states: 'Check spendable USD balance for a card alias' — this is a query operation that retrieves balance information with no side effects or modification.
Attacks that exploit this kind of access
Check spendable USD balance for a card alias. For active token limits, use list_cards instead. It is categorised as a Read tool in the Z Zero MCP Server, which means it retrieves data without modifying state.
check_balance accepts 1 parameter: card_alias. Required: card_alias. The full parameter table on this page comes from the server's own tool schema.
Register the Z Zero MCP server in PolicyLayer and add a rule for check_balance: 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 Z Zero. Nothing to install.
check_balance is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the check_balance 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 check_balance. 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.
check_balance is provided by the Z Zero MCP server (z-zero-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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