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Compound Interest Calculator

calc_interest
Read-onlyIdempotent

Calculate the future value of an investment using compound interest. Input principal, annual rate, time, and compounding frequency.

Instructions

Calculate compound interest for investments.

Formula: A = P(1 + r/n)^(nt) Where:

  • P = principal amount

  • r = annual interest rate (as decimal)

  • n = number of times interest compounds per year

  • t = time in years

Examples: compound_interest(10000, 0.05, 5) # $10,000 at 5% for 5 years → $12,762.82 compound_interest(5000, 0.03, 10, 12) # $5,000 at 3% compounded monthly → $6,744.25

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
rateYesAnnual interest rate as decimal 0.0-1.0 (e.g. 0.05 = 5%). If entering a percentage, divide by 100 first.
timeYesInvestment time in years (must be > 0), e.g. 10.0
principalYesInitial investment amount in dollars (must be > 0), e.g. 1000.0
compounds_per_yearNoCompounding frequency per year (must be > 0): 12=monthly, 365=daily

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
rateYes
timeYes
topicYes
formulaYes
principalYes
difficultyYes
final_amountYes
total_interestYes
compounds_per_yearYes
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true and idempotentHint=true, so the description does not need to reiterate safety. It adds value by detailing the formula and parameter constraints (e.g., rate as decimal), providing more context than the annotations alone.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is well-structured with purpose, formula, and examples. It is slightly verbose but efficient, with no redundant information. The front-loading of purpose helps agents quickly understand the tool.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the existence of an output schema, return values do not need explanation. The description adequately covers input parameters and usage. It does not discuss error handling or edge cases, but for a simple calculator, this is sufficient.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so baseline is 3. The description adds examples that demonstrate parameter usage, such as default compounds_per_year=12 and rate conversion. This enhances understanding beyond the schema descriptions.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

Description explicitly states 'Calculate compound interest for investments' with a clear formula and examples. It distinguishes itself from sibling tools like calc_expression or calc_statistics by being specific to compound interest calculations.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description does not provide explicit guidance on when to use this tool versus alternatives. While the purpose is clear, there's no mention of when not to use it or comparisons to sibling tools. The usage context is implied but not stated.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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