OnlineCyberTools MCP (280+ filterable tools)

math_compound_interest_calculator

Read-onlyIdempotent

Calculate the future value of a lump-sum investment with compound interest and recurring contributions. Get final balance, total interest, and per-period breakdown.

Instructions

Compound Interest Calculator. Project the future value of a lump-sum principal growing at a fixed annual rate with periodic (per-compounding-period) compounding and optional recurring contributions. Returns the final balance, total interest earned, total contributions, and a per-period or per-year breakdown. Use this for savings/investment growth ("how much will X grow to in N years"); use math_loan_calculator instead when you owe a balance and need a monthly payment + amortization schedule, or math_percentage_calculator for one-off percent-of / percent-change math. Pure local arithmetic: read-only, non-destructive, deterministic, contacts no external service, and is rate-limited.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`operation`	No	"compute" returns a per-year breakdown (one row per year); "schedule" returns the full per-period schedule (one row per compounding period). Both return the same final totals.	compute
`principal`	Yes	Starting lump-sum amount (P). 0 to 1,000,000,000,000.
`annualRatePercent`	Yes	Nominal annual interest rate as a percent (e.g. 5 means 5%/yr). 0 to 100.
`years`	Yes	Investment horizon in years (t). Greater than 0, up to 100; may be fractional.
`compoundingsPerYear`	Yes	Compounding frequency per year (n): 1=annual, 2=semi-annual, 4=quarterly, 12=monthly, 365=daily. Must be exactly one of these values.
`monthlyContribution`	No	Optional recurring monthly contribution. Converted to a per-compounding-period amount (monthlyContribution × 12 / compoundingsPerYear) so the same annual dollar flow applies at any frequency. 0 to 1,000,000,000.
`contributionTiming`	No	Whether each contribution is applied at the start (annuity-due) or end (ordinary annuity) of the period. Only relevant when monthlyContribution > 0.	end

Output Schema

TableJSON Schema

Name	Required	Description
`success`	No	True when the calculation succeeded.
`operation`	No	Echoes the operation that was run.
`result`	No	Computed totals plus a breakdown (compute) or schedule (schedule) array.

Schema Changelog

Changes observed during successful MCP inspections.

Changed33 schema fields changedv0.5.1Jun 3, 2026

addedInput schema / additionalProperties
```
Added value: +false
```

addedInput schema / properties / annualRatePercent / description

Added value: +"Nominal annual interest rate as a percent (e.g. 5 means 5%/yr). 0 to 100."

addedInput schema / properties / annualRatePercent / examples
```
Added value: +[
+  5
+]
```
addedInput schema / properties / annualRatePercent / maximum
```
Added value: +100
```
addedInput schema / properties / annualRatePercent / minimum
```
Added value: +0
```
changedInput schema / properties / annualRatePercent / type
```
Previous value: -"integer"New value: +"number"
```

addedInput schema / properties / compoundingsPerYear / description

Added value: +"Compounding frequency per year (n): 1=annual, 2=semi-annual, 4=quarterly, 12=monthly, 365=daily. Must be exactly one of these values."

addedInput schema / properties / compoundingsPerYear / enum
```
Added value: +[
+  1,
+  2,
+  4,
+  12,
+  365
+]
```
addedInput schema / properties / compoundingsPerYear / examples
```
Added value: +[
+  12
+]
```
addedInput schema / properties / contributionTiming / default
```
Added value: +"end"
```

addedInput schema / properties / contributionTiming / description

Added value: +"Whether each contribution is applied at the start (annuity-due) or end (ordinary annuity) of the period. Only relevant when monthlyContribution > 0."

addedInput schema / properties / contributionTiming / enum
```
Added value: +[
+  "start",
+  "end"
+]
```
addedInput schema / properties / monthlyContribution / default
```
Added value: +0
```

addedInput schema / properties / monthlyContribution / description

Added value: +"Optional recurring monthly contribution. Converted to a per-compounding-period amount (monthlyContribution × 12 / compoundingsPerYear) so the same annual dollar flow applies at any frequency. 0 to 1,000,000,000."

addedInput schema / properties / monthlyContribution / examples
```
Added value: +[
+  200
+]
```
addedInput schema / properties / monthlyContribution / maximum
```
Added value: +1000000000
```
addedInput schema / properties / monthlyContribution / minimum
```
Added value: +0
```
changedInput schema / properties / monthlyContribution / type
```
Previous value: -"integer"New value: +"number"
```
addedInput schema / properties / operation / default
```
Added value: +"compute"
```

addedInput schema / properties / operation / description

Added value: +"\"compute\" returns a per-year breakdown (one row per year); \"schedule\" returns the full per-period schedule (one row per compounding period). Both return the same final totals."

addedInput schema / properties / operation / enum

Added value: +[
+  "compute",
+  "schedule"
+]

addedInput schema / properties / principal / description

Added value: +"Starting lump-sum amount (P). 0 to 1,000,000,000,000."

addedInput schema / properties / principal / examples
```
Added value: +[
+  10000
+]
```
addedInput schema / properties / principal / maximum
```
Added value: +1000000000000
```
addedInput schema / properties / principal / minimum
```
Added value: +0
```
changedInput schema / properties / principal / type
```
Previous value: -"integer"New value: +"number"
```

addedInput schema / properties / years / description

Added value: +"Investment horizon in years (t). Greater than 0, up to 100; may be fractional."

addedInput schema / properties / years / examples
```
Added value: +[
+  10
+]
```
addedInput schema / properties / years / exclusiveMinimum
```
Added value: +0
```
addedInput schema / properties / years / maximum
```
Added value: +100
```

changedInput schema / properties / years / type

Previous value: -"integer"New value: +"number"

changedInput schema / required

Previous value: -[
-  "operation",
-  "principal",
-  "annualRatePercent",
-  "years",
-  "compoundingsPerYear",
-  "monthlyContribution",
-  "contributionTiming"
-]New value: +[
+  "principal",
+  "annualRatePercent",
+  "years",
+  "compoundingsPerYear"
+]

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "operation": {
+      "description": "Echoes the operation that was run.",
+      "enum": [
+        "compute",
+        "schedule"
+      ],
+      "type": "string"
+    },
+    "result": {
+      "description": "Computed totals plus a breakdown (compute) or schedule (schedule) array.",
+      "properties": {
+        "breakdown": {
+          "description": "Per-year summary. Present when operation=compute.",
+          "items": {
+            "properties": {
+              "balance": {
+                "description": "Balance at the end of this year.",
+                "type": "number"
+              },
+              "contributionsToDate": {
+                "description": "Cumulative contributions made through this year.",
+                "type": "number"
+              },
+              "interestEarned": {
+                "description": "Cumulative interest earned through this year.",
+                "type": "number"
+              },
+              "year": {
+                "description": "1-based year index.",
+                "type": "integer"
+              }
+            },
+            "type": "object"
+          },
+          "type": "array"
+        },
+        "finalAmount": {
+          "description": "Final balance after the full term, rounded to 2 decimals.",
+          "type": "number"
+        },
+        "schedule": {
+          "description": "Per-compounding-period rows. Present when operation=schedule.",
+          "items": {
+            "properties": {
+              "balance": {
+                "description": "Balance at the end of this period.",
+                "type": "number"
+              },
+              "contribution": {
+                "description": "Total contribution applied in this period.",
+                "type": "number"
+              },
+              "interest": {
+                "description": "Interest earned in this period.",
+                "type": "number"
+              },
+              "period": {
+                "description": "1-based period index (1 .. years × compoundingsPerYear).",
+                "type": "integer"
+              }
+            },
+            "type": "object"
+          },
+          "type": "array"
+        },
+        "totalContributions": {
+          "description": "Sum of all recurring contributions over the term, rounded to 2 decimals.",
+          "type": "number"
+        },
+        "totalInterest": {
+          "description": "Total interest earned over the term, rounded to 2 decimals.",
+          "type": "number"
+        }
+      },
+      "type": "object"
+    },
+    "success": {
+      "description": "True when the calculation succeeded.",
+      "type": "boolean"
+    }
+  },
+  "type": "object"
+}

First observedv0.1.0May 31, 2026

TDQS

A4.9/5.0

Behavior5/5

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

Annotations already indicate read-only, non-destructive, idempotent. The description adds 'deterministic', 'contacts no external service', and 'rate-limited', providing useful context beyond annotations. No contradiction.

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

Conciseness5/5

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

5 sentences, no fluff. Front-loads purpose, then output, usage guidelines, and behavioral traits. Every sentence earns its place. Highly efficient.

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

Completeness5/5

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

Given the tool's moderate complexity with 7 parameters and existing output schema, the description covers purpose, usage, behavior, and output summary. No gaps remain for agent decision-making.

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% with detailed descriptions for each parameter. The description adds value by summarizing outputs (final balance, interest, etc.) and explaining operation parameter semantics. This goes beyond baseline 3.

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?

The description clearly states the tool's purpose: projecting future value of a lump-sum with fixed rate, periodic compounding, and optional contributions. It distinguishes itself from siblings like math_loan_calculator and math_percentage_calculator, making scope explicit.

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

Usage Guidelines5/5

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

Explicitly provides when-to-use (savings/investment growth) and when-not-to-use (use math_loan_calculator for loans, math_percentage_calculator for percent calculations). This leaves no ambiguity for the agent.

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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