Amaltash Investment & Retirement Calculators

S&P 500 Return Calculator

sp500_since_date

Read-onlyIdempotent

S&P 500 return calculator with an interactive chart. Shows what a set amount in the S&P 500 would have become between two years from 1928 to 2025, using real yearly returns. It also gives the amount put in after inflation and the worst year in the span.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "amount": "<amount>",
      "cadence": "<cadence>",
      "from_year": "<from_year>",
      "to_year": "<to_year>"
    },
    "name": "sp500_since_date"
  }
}

Input Schema

Name	Required	Description
`amount`	Yes	Dollars invested each time.
`cadence`	Yes	How often the money goes in: day, week, month, year, or once.
`to_year`	Yes	Last year, included, from 1928 to 2025. Cannot be before from_year.
`from_year`	Yes	First year, from 1928 to 2025.

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 10, 2026

TDQS

A3.7/5.0

Behavior4/5

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

Annotations already establish that this is a safe, read-only, idempotent, non-destructive, closed-world calculation. The description adds useful behavioral context beyond those annotations: it explains that real yearly returns are used and that results include the after-inflation amount and the worst year in the span. It does not describe the chart interaction or calculation assumptions in detail.

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 two sentences, front-loaded with the calculator purpose and followed by the output details. It is efficient, though the interactive chart mention is slightly peripheral to tool selection.

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?

For a four-parameter read-only calculator with no output schema, the description sufficiently explains the calculation basis and key outputs. It does not cover every nuance of cadence or chart behavior, but it gives an agent enough context to invoke the tool correctly.

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

Parameters3/5

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 amount, cadence, from_year, and to_year. The description reinforces the amount and two-year span but adds no syntax or meaning for cadence beyond what the schema provides. A baseline score of 3 is appropriate.

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

Purpose4/5

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

The description uses a specific verb and resource: it calculates what a set amount invested in the S&P 500 would have become between two years using real yearly returns. It also names the extra outputs (inflation-adjusted amount and worst year). It does not distinguish this tool from sibling calculators such as compound_interest or dca_vs_lump_sum.

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?

Usage is implied by the historical S&P 500 scope and the 1928-2025 range, but there is no explicit guidance on when to choose this tool over sibling calculators. No exclusions or alternative routing is provided.

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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