AI agents call present_value to retrieve information from TinyFn without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
| Parameter | Type | Required | Description |
|---|---|---|---|
rate | number | Yes | Annual discount rate (percentage) |
years | integer | Yes | Number of years |
future_value | number | Yes | Future value |
Parameters from the server's own tool schema.
This is a financial calculation tool that performs a deterministic mathematical formula (present value = future value / (1 + rate)^periods or similar). It retrieves no data, modifies nothing, executes no external operations, and produces no side effects. While the domain is financial, the tool itself merely computes and returns a value—it does not move money, create obligations, or change system state.
From the tool's definition Tool name 'present_value' and description 'Calculate present value of a future amount' indicate a pure calculation/query operation with no side effects.
Attacks that exploit this kind of access
Calculate present value of a future amount. It is categorised as a Read tool in the TinyFn MCP Server, which means it retrieves data without modifying state.
present_value accepts 3 parameters: rate, years, future_value. Required: rate, years, future_value. The full parameter table on this page comes from the server's own tool schema.
Register the TinyFn MCP server in PolicyLayer and add a rule for present_value: 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 TinyFn. Nothing to install.
present_value 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 present_value 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 present_value. 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.
present_value is provided by the TinyFn MCP server (https://api.tinyfn.io/mcp/all/). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
present_value is one line of TinyFn's registry record.
The record carries the whole server: verified identity, auth posture, risk grade, every tool classified, recommended policy — re-checked continuously.
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