Biorhythm MCP Server by RoxyAPI

Find critical days - Zero crossing detection for any date range

post_biorhythm_critical_days

Read-only

Find all critical days (zero crossings) within a date range up to 180 days. Returns each critical day with cycle name, period, direction (ascending or descending), severity (single, double, or triple), and advisory text. Highlights rare double critical days where two primary cycles cross zero simultaneously and extremely rare triple critical days where all three primary cycles cross zero on the same date. Ideal for calendar integrations, push notification systems, alert engines, and wellness scheduling tools.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`lang`	No	Response language (BCP 47). Supported: en, tr, de, es, hi, pt, fr, ru, zh-Hans, zh-Hant. Defaults to en. Coverage varies by domain, and a field with no translation in the requested language returns English.	en
`compact`	No	Set true for the same data in a compact shape: arrays of same-shaped objects arrive columnar as {"__cols":[names],"__rows":[[values]]}. Lossless, typically 40 to 52 percent fewer tokens.
`endDate`	No	End date of the search range in YYYY-MM-DD format. Defaults to startDate + 90 days. Maximum range: 180 days.
`birthDate`	Yes	Birth date of the person in YYYY-MM-DD format.
`startDate`	No	Start date of the search range in YYYY-MM-DD format. Defaults to today (UTC).

Output Schema

TableJSON Schema

Name	Required	Description	Default
`endDate`	Yes
`birthDate`	Yes
`startDate`	Yes
`criticalDays`	Yes
`totalCriticalDays`	Yes
`tripleCriticalDay`	Yes
`doubleCriticalDays`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 20, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "birthDate": {
+      "type": "string"
+    },
+    "criticalDays": {
+      "items": {
+        "properties": {
+          "advisory": {
+            "type": "string"
+          },
+          "cycle": {
+            "enum": [
+              "physical",
+              "emotional",
+              "intellectual"
+            ],
+            "type": "string"
+          },
+          "date": {
+            "type": "string"
+          },
+          "direction": {
+            "enum": [
+              "ascending",
+              "descending"
+            ],
+            "type": "string"
+          },
+          "period": {
+            "type": "number"
+          },
+          "severity": {
+            "enum": [
+              "single",
+              "double",
+              "triple"
+            ],
+            "type": "string"
+          }
+        },
+        "required": [
+          "date",
+          "cycle",
+          "period",
+          "direction",
+          "severity",
+          "advisory"
+        ],
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "doubleCriticalDays": {
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
+    "endDate": {
+      "type": "string"
+    },
+    "startDate": {
+      "type": "string"
+    },
+    "totalCriticalDays": {
+      "type": "number"
+    },
+    "tripleCriticalDay": {
+      "type": [
+        "string",
+        "null"
+      ]
+    }
+  },
+  "required": [
+    "birthDate",
+    "startDate",
+    "endDate",
+    "totalCriticalDays",
+    "criticalDays",
+    "doubleCriticalDays",
+    "tripleCriticalDay"
+  ],
+  "type": "object"
+}

Changed2 schema fields changedAug 25, 2026

changedInput schema / properties / lang / description

Previous value: -"Response language (ISO 639-1). Supported: en, tr, de, es, hi, pt, fr, ru. Defaults to en. Languages without translations yet return English."New value: +"Response language (BCP 47). Supported: en, tr, de, es, hi, pt, fr, ru, zh-Hans, zh-Hant. Defaults to en. Coverage varies by domain, and a field with no translation in the requested language returns English."

changedInput schema / properties / lang / enum

Previous value: -[
-  "en",
-  "tr",
-  "de",
-  "es",
-  "hi",
-  "pt",
-  "fr",
-  "ru"
-]New value: +[
+  "en",
+  "tr",
+  "de",
+  "es",
+  "hi",
+  "pt",
+  "fr",
+  "ru",
+  "zh-Hans",
+  "zh-Hant"
+]

Changed2 schema fields changedAug 17, 2026

addedInput schema / examples

Added value: +[
+  {
+    "birthDate": "1990-07-15"
+  }
+]

changedInput schema / properties / compact / description

Previous value: -"Set true to receive the exact same data in a token-optimized shape that is cheaper for you to read: whitespace is stripped and every array of same-shaped objects is encoded columnar as {\"__cols\":[field names],\"__rows\":[[values]]}, so each field name is sent once instead of once per row. Fully lossless (no field or value is dropped or changed) and typically 40 to 52 percent fewer tokens on large results. Prefer true whenever token or inference cost matters. Default false returns standard indented JSON."New value: +"Set true for the same data in a compact shape: arrays of same-shaped objects arrive columnar as {\"__cols\":[names],\"__rows\":[[values]]}. Lossless, typically 40 to 52 percent fewer tokens."

Changed1 schema field changedJul 22, 2026

changedInput schema / properties / compact / description

Previous value: -"Return the same data in a token-optimized compact shape (minified, with same-shaped arrays encoded columnar) to reduce LLM token cost. Lossless: no fields are dropped. Default false."New value: +"Set true to receive the exact same data in a token-optimized shape that is cheaper for you to read: whitespace is stripped and every array of same-shaped objects is encoded columnar as {\"__cols\":[field names],\"__rows\":[[values]]}, so each field name is sent once instead of once per row. Fully lossless (no field or value is dropped or changed) and typically 40 to 52 percent fewer tokens on large results. Prefer true whenever token or inference cost matters. Default false returns standard indented JSON."

Changed1 schema field changedJul 22, 2026

addedInput schema / properties / compact

Added value: +{
+  "default": false,
+  "description": "Return the same data in a token-optimized compact shape (minified, with same-shaped arrays encoded columnar) to reduce LLM token cost. Lossless: no fields are dropped. Default false.",
+  "type": "boolean"
+}

First observedJul 8, 2026

TDQS

A4.5/5.0

Behavior5/5

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

Beyond the readOnlyHint and destructiveHint annotations, the description discloses meaningful behavior: it returns cycle name, period, direction, severity, and advisory text, and it highlights rare double and triple critical days. This gives the agent a clear picture of what the tool produces without relying on the output schema.

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 sentences with the primary purpose front-loaded. Each sentence adds value: scope, output contents, and especially notable edge cases. No filler or repetition.

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?

For a read-only lookup tool with rich schema coverage and an output schema, the description is complete: it states the range cap, the output fields, the severity taxonomy, and the practical use cases. An agent has enough to select and invoke this 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 input schema fully documents birthDate, startDate, endDate, lang, and compact. The description's mention of the 180-day range reinforces the schema but does not add parameter-level meaning beyond it. Baseline 3 is appropriate.

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 opens with a specific verb and resource: 'Find all critical days (zero crossings) within a date range.' It names the exact output content and clearly differentiates this from sibling tools like daily, forecast, phases, compatibility, and reading by focusing on zero-crossing critical-day detection.

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

Usage Guidelines4/5

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

The description gives clear context for when to use the tool: date-range-based zero-crossing detection up to 180 days, ideal for calendar integrations, notifications, alert engines, and wellness scheduling. It does not explicitly name sibling alternatives or state when not to use it, so it stops short of a 5.

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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