Menstrual Cycle Skill
The tool
The API generates detailed cycle calendars with phase information including menstruation, follicular, ovulation, and luteal phases for multiple upcoming cycles.
Once your client is connected to the VerveKit MCP server, this appears in its tool list as MenstrualCycleSkill. It is read-only and open-world: it fetches, it never mutates anything on your side, so most clients will call it without asking you to confirm.
{
"name": "MenstrualCycleSkill",
"arguments": {
"last_period": "2024-01-01"
}
}What that looks like in a conversation
You don't name the tool — the model picks it. Asking about 2024-01-01 in the terms this source covers is enough for it to reach for MenstrualCycleSkill on its own.
Connecting
One server URL covers every skill in the catalog, including this one. Authorization is OAuth — the client opens a browser once and there is no key to paste into a config file.
{
"mcpServers": {
"vervekit": {
"url": "https://api.vervekit.com/v1/mcp"
}
}
}https://api.vervekit.com/v1/mcpPer-client setup — Claude Desktop, Cursor, VS Code, ChatGPT — is on the MCP setup page.
Arguments
These are the properties on the tool's inputSchema, so a well-behaved client validates them before the call is made.
| Argument | Type | Example | Description |
|---|---|---|---|
last_periodRequired | string | 2024-01-01 | First day of last menstrual period (YYYY-MM-DD) |
cycle_length | integer | 28 | Average cycle length in days |
period_length | integer | 5 | Average period duration in days |
cycles | integer | 3 | Number of future cycles to calculate |
What the model gets back
The result carries a structuredContent object matching the tool's declared outputSchema, so a client can read fields without parsing prose. status is "ok" on success and error is null; a null field means the value wasn't available for that input, not that the call failed.
{
"status": "ok",
"error": null,
"data": {
"last_period_date": "2024-01-01",
"cycle_length": 28,
"period_length": 5,
"cycles_calculated": 3,
"cycles": [
{
"cycle_number": 1,
"period": {
"start_date": "2024-01-01",
"end_date": "2024-01-05",
"duration_days": 5
},
"ovulation": {
"date": "2024-01-15",
"day_of_cycle": 14
},
"fertile_window": {
"start_date": "2024-01-10",
"end_date": "2024-01-15",
"duration_days": 6
},
"pms_phase": {
"start_date": "2023-12-21",
"end_date": "2023-12-31"
},
"cycle_phases": {
"menstrual": {
"start": "2024-01-01",
"end": "2024-01-05",
"description": "Menstruation"
},
"follicular": {
"start": "2024-01-06",
"end": "2024-01-14",
"description": "Follicular phase - preparing for ovulation"
},
"ovulation": {
"date": "2024-01-15",
"description": "Ovulation - most fertile day"
},
"luteal": {
"start": "2024-01-16",
"end": "2024-01-28",
"description": "Luteal phase - preparing for next period"
}
},
"status": "past",
"days_until": null,
"days_ago": 715
},
{
"cycle_number": 2,
"period": {
"start_date": "2024-01-29",
"end_date": "2024-02-02",
"duration_days": 5Fields
| Field | Type | Example | Description |
|---|---|---|---|
last_period_date | string | 2024-01-01 | First day of last menstrual period |
cycle_length | number | 28 | Average menstrual cycle length in days |
period_length | number | 5 | Average menstrual period duration in days |
cycles_calculated | number | 3 | Total number of cycles calculated |
cycles | array[3] | list of rows | Array of calculated menstrual cycles with details |
cycles.0.cycle_number | number | 1 | |
cycles.0.period | object | {…} | |
cycles.0.period.start_date | string | 2024-01-01 | |
cycles.0.period.end_date | string | 2024-01-05 | |
cycles.0.period.duration_days | number | 5 | |
cycles.0.ovulation | object | {…} | |
cycles.0.ovulation.date | string | 2024-01-15 | |
cycles.0.ovulation.day_of_cycle | number | 14 | |
cycles.0.fertile_window | object | {…} | |
cycles.0.fertile_window.start_date | string | 2024-01-10 | |
cycles.0.fertile_window.end_date | string | 2024-01-15 | |
cycles.0.fertile_window.duration_days | number | 6 | |
cycles.0.pms_phase | object | {…} | |
cycles.0.pms_phase.start_date | string | 2023-12-21 | |
cycles.0.pms_phase.end_date | string | 2023-12-31 | |
cycles.0.cycle_phases | object | {…} | |
cycles.0.cycle_phases.menstrual | object | {…} | |
cycles.0.cycle_phases.menstrual.start | string | 2024-01-01 | |
cycles.0.cycle_phases.menstrual.end | string | 2024-01-05 | |
cycles.0.cycle_phases.menstrual.description | string | Menstruation | |
cycles.0.cycle_phases.follicular | object | {…} | |
cycles.0.cycle_phases.follicular.start | string | 2024-01-06 | |
cycles.0.cycle_phases.follicular.end | string | 2024-01-14 | |
cycles.0.cycle_phases.follicular.description | string | Follicular phase - preparing for ovulation | |
cycles.0.cycle_phases.ovulation | object | {…} | |
cycles.0.cycle_phases.ovulation.date | string | 2024-01-15 | |
cycles.0.cycle_phases.ovulation.description | string | Ovulation - most fertile day | |
cycles.0.cycle_phases.luteal | object | {…} | |
cycles.0.cycle_phases.luteal.start | string | 2024-01-16 | |
cycles.0.cycle_phases.luteal.end | string | 2024-01-28 | |
cycles.0.cycle_phases.luteal.description | string | Luteal phase - preparing for next period | |
cycles.0.status | string | past | |
cycles.0.days_until | object | null | |
cycles.0.days_ago | number | 715 | |
current_status | object | {…} | Which phase today falls in and when the next period is due |
current_status.phasePremium | string | Unknown | Current menstrual cycle phase name |
current_status.descriptionPremium | string | | Description of current cycle phase |
current_status.next_periodPremium | object | null | Date of next expected menstrual period |
current_status.days_until_next_periodPremium | object | null | Days until next menstrual period starts |
averages | object | {…} | Average cycle length, period duration and gap between periods |
averages.cycle_lengthPremium | number | 28 | Average menstrual cycle length across periods |
averages.period_durationPremium | number | 5 | Average menstrual period duration across cycles |
averages.days_between_periodsPremium | number | 28 | Average days between menstrual period starts |
disclaimer | string | This calculator provides estimates only. Actual cycles may vary. Consult a healthcare provider for medical advice. | Legal disclaimer about calculation accuracy |
Failure modes
Errors come back as tool errors with a sentence the model can act on, not a bare status code.
| Status | What it means |
|---|---|
400 / 422 | The arguments didn't validate. The message names the offending one. |
401 | The OAuth session is invalid or expired — reconnect the server. |
403 | Out of credits. Not a bad key — the month's allowance is spent. |
404 | This skill isn't part of VerveKit. Check the catalog. |
429 | Brief rate limit. Retrying after a moment succeeds. |
Other ways to use Menstrual Cycle Skill
Set up Menstrual Cycle Skill on VerveKit, or reach the same source a different way. Your VerveKit account and credits work on all of them — one key, one balance.
Frequently asked questions
Do I have to tell the agent to use MenstrualCycleSkill?
No. The tool's name and description are in the model's context once the server is connected, so it selects the tool when the question calls for it. Naming it explicitly works too and is useful when you want to force the call.
Does connecting the server expose every tool at once?
Yes — one connection lists the whole VerveKit catalog. Clients with a tool budget can usually filter the list; the credit cost is per call, so an unused tool costs nothing.
What does a call cost?
1 credit each time the tool actually runs. A model that reasons about the tool without calling it costs nothing.
Is there a REST version of this?
Yes — the same source is available as a plain HTTPS endpoint on APIVerve, linked above. Same data, same credits, same account.