This record as markdown: /tools/io-tinyfn-tinyfn/simple-interest.md
What simple_interest does on TinyFn
AI agents call simple_interest to retrieve information from TinyFn without modifying anything. It is 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 interest rate (percentage) |
time | number | Yes | Time in years |
principal | number | Yes | Initial principal |
Parameters from the server's own tool schema.
Why simple_interest is rated Low
This is a deterministic computational tool that performs a mathematical formula (I = P × R × T). It reads input values and returns a calculated result. No state is modified, no external operations are triggered, and no irreversible actions occur. While it relates to financial concepts, it merely computes a theoretical value rather than moving money or committing financial obligations, placing it in the Read category.
From the tool's definition Tool name 'simple_interest' and description 'Calculate simple interest' indicate a pure mathematical calculation with no side effects.
Attacks that exploit this kind of access
The rule that runs simple_interest safely
PolicyLayer is an MCP gateway: it sits between your AI agents and TinyFn, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For simple_interest, this is the rule to start with:
simple_interest is read-only, so it stays allowed. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect TinyFn, apply this rule, and every simple_interest call is checked against it from then on.
Questions about simple_interest
Calculate simple interest. It is categorised as a Read tool in the TinyFn MCP Server, which means it retrieves data without modifying state.
simple_interest accepts 3 parameters: rate, time, principal. Required: rate, time, principal. 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 simple_interest: 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.
simple_interest 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 simple_interest 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 simple_interest. 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.
simple_interest 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.
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