> ## Documentation Index
> Fetch the complete documentation index at: https://docs.fincept.in/llms.txt
> Use this file to discover all available pages before exploring further.

# Core Module

> Dates, calendars, financial types - FREE tier

# Core Module

**Tier:** Free | **Cost:** 0 credits | **Endpoints:** 51

Essential date handling, calendars, and financial utilities.

## Key Features

* Business day checks (50+ calendars)
* Date arithmetic with tenors
* Day count conventions
* Pure Black-Scholes pricing
* Automatic differentiation
* Financial type operations

## Popular Endpoints

**Check Business Day:**

```bash theme={null}
POST /quantlib/core/date/is-business-day
{"date": "2024-01-15", "calendar": "UnitedStates"}
```

**Add Tenor:**

```bash theme={null}
POST /quantlib/core/types/tenor/add-to-date
{"date": "2024-01-15", "tenor": "3M"}
```

**Black-Scholes:**

```bash theme={null}
POST /quantlib/core/pure/black-scholes
{"spot": 100, "strike": 105, "rate": 0.05, "volatility": 0.2, "time": 0.25}
```

[Full API Reference →](/api-reference/quantlib-core)