EveryCalc

calculate_date_duration

Read-onlyIdempotent

Inclusive number of days between two dates, plus business days after optionally excluding weekends and 2026 US federal holidays, calendar weeks, weekend days, and holidays in the range. Use when the user needs the days or business days between two dates. For age from a birth date use calculate_age. 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 date duration calculator calculator.

Input Schema

Name	Required	Description
`end_date`	Yes	End date in YYYY-MM-DD format.
`start_date`	Yes	Start date in YYYY-MM-DD format.
`exclude_holidays`	No	Exclude 2026 US federal holidays from the business day count.
`exclude_weekends`	No	Exclude Saturdays and Sundays from the business day count. The page has this checked by default.

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

A4.1/5.0

Behavior4/5

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

Annotations already cover the read-only/idempotent/non-destructive profile, and the description adds real behavioral context: counts are inclusive, holidays are limited to 2026 US federal holidays, and the result carries a calculator_url that must be surfaced as a markdown link. The garbled enumeration of "calendar weeks, weekend days, and holidays" is a minor clarity cost.

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

Conciseness3/5

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

The purpose sentence is overloaded and reads as a garbled list, and the closing instruction contains a duplicated phrase ("calculator calculator"). The routing guidance is front-loaded and the IMPORTANT callout is justified, but the prose needs editing to be scannable.

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?

With an output schema present, return values need not be explained, and the description still covers purpose, trigger, alternative, counting convention, and the required link-display behavior. Only the ambiguous trailing enumeration of returned figures keeps it short of full completeness.

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 the baseline is 3, but the description adds semantics the schema does not: inclusive endpoint counting, the 2026-only holiday scope, and that the page defaults to excluding weekends. Those details change how an agent interprets the boolean parameters' effect on results.

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?

States a specific verb+resource (day/business-day count between two dates) and explicitly separates itself from the sibling calculate_age. The opening clause is a run-on that muddles what is returned versus what is excluded, but the core purpose is still unambiguous.

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?

"Use when the user needs the days or business days between two dates" gives the trigger condition, and "For age from a birth date use calculate_age" names the alternative and the condition that selects it. Routing guidance is explicit rather than implied.

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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