EveryCalc

calculate_401k

Read-onlyIdempotent

Projected 401k balance with employee contributions capped at 24500 per year, plus an employer match, compounded annually. Use when the user projects a 401k with contributions and an employer match. For a general investment projection use calculate_compound_interest; for TSP use calculate_tsp. IMPORTANT: always show the calculator_url from the result as a clickable markdown link in your answer to the user, so they can open the interactive 401k calculator.

Input Schema

Name	Required	Description
`years`	Yes	Years to project.
`match_pct`	Yes	Employer match percent of the matched contribution.
`annual_salary`	Yes	Annual salary in USD.
`match_cap_pct`	Yes	Percent of salary eligible for the employer match.
`current_balance`	Yes	Current 401k balance in USD.
`contribution_pct`	Yes	Employee contribution percent of salary.
`annual_return_pct`	Yes	Annual return percent.

Output Schema

Name	Required	Description
`ok`	Yes	True when the calculation succeeded.
`note`	Yes	Disclaimer that accompanies every result.
`tool`	Yes	Name of the tool that ran.
`inputs`	No	The normalized inputs the calculation used.
`results`	Yes	The computed figures for this calculator.
`calculator_url`	Yes	Deep link to the matching interactive calculator on everycalc.xyz.

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 21, 2026

addedOutput schema / properties / note

Added value: +{
+  "description": "Disclaimer that accompanies every result.",
+  "type": "string"
+}

changedOutput schema / required

Previous value: -[
-  "ok",
-  "tool",
-  "results",
-  "calculator_url"
-]New value: +[
+  "ok",
+  "tool",
+  "results",
+  "calculator_url",
+  "note"
+]

Changed1 schema field changedOct 17, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "calculator_url": {
+      "description": "Deep link to the matching interactive calculator on everycalc.xyz.",
+      "type": "string"
+    },
+    "inputs": {
+      "description": "The normalized inputs the calculation used.",
+      "type": "object"
+    },
+    "ok": {
+      "description": "True when the calculation succeeded.",
+      "type": "boolean"
+    },
+    "results": {
+      "description": "The computed figures for this calculator.",
+      "type": "object"
+    },
+    "tool": {
+      "description": "Name of the tool that ran.",
+      "type": "string"
+    }
+  },
+  "required": [
+    "ok",
+    "tool",
+    "results",
+    "calculator_url"
+  ],
+  "type": "object"
+}

First observedOct 15, 2026

TDQS

A4.7/5.0

Behavior4/5

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

Annotations already declare read-only, idempotent, non-destructive, and closed-world behavior, so the description needn't repeat safety traits. Beyond that, it discloses calculation behavior (annual compounding, a $24,500 employee contribution cap, employer match) and a critical output-handling requirement: the calculator_url must be shown as a clickable markdown link. It does not cover error handling or validation edge cases, which keeps it from a 5.

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?

The description is three tight sentences plus a clearly marked IMPORTANT instruction. The purpose is front-loaded, the alternatives are named early, and the output instruction is separated for emphasis. Every sentence carries information needed to select or correctly use the tool.

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?

Although an output schema exists, the description still highlights the calculator_url and how to present it, which is not captured in the output schema. It also covers calculation methodology, when to use the tool, and alternatives. For a 7-parameter financial calculator with rich annotations, this is complete enough for correct invocation.

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 description coverage is 100%, so the schema already documents all seven parameters, setting the baseline at 3. The description adds domain meaning beyond the schema: the $24,500 annual employee contribution cap, the presence of an employer match, and annual compounding. It does not explain how match_pct and match_cap_pct interact, but the extra cap rule justifies a 4.

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 states a specific verb and resource: projecting a 401k balance with employee contributions and an employer match, compounded annually. It explicitly differentiates from siblings by naming calculate_compound_interest for general investment projections and calculate_tsp for TSP. An agent can select this tool correctly without opening the schema.

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?

It gives explicit when-to-use guidance ('Use when the user projects a 401k with contributions and an employer match') and concrete alternatives for when not to use it ('calculate_compound_interest', 'calculate_tsp'). The instruction to show the calculator_url is an additional output-handling guideline that further constrains proper usage.

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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