# Overview (/en/docs/guide/getting-started)

The inputs a chart needs, what each parameter accepts, and how to install for each of the three programming languages.



*For: everyone. The parameter table is readable without writing code*

All three bindings share one Rust core, so parameter meanings and chart results are identical —
only the spelling differs. Get clear on what you need to supply, then pick your programming
language.

## The inputs you need [#the-inputs-you-need]

Whatever the programming language, charting starts from these parameters. The first three are
required; the last three have defaults.

| Parameter                   | Meaning                 | Accepts                                                                          |
| --------------------------- | ----------------------- | -------------------------------------------------------------------------------- |
| `solar_date` / `lunar_date` | Date of birth           | `"YYYY-M-D"`, e.g. `"2000-8-16"`. Gregorian range 1583–9999                      |
| `time_index`                | Hour of birth           | Integer 0–12, see the table below                                                |
| `gender`                    | Gender                  | `"male"` / `"female"` (a `Gender` enum in Rust)                                  |
| `fix_leap`                  | Correct for leap months | Boolean, defaults to `true`                                                      |
| `language`                  | Chart language          | `"zh-CN"` (default), `"zh-TW"`, `"en-US"`, `"ja-JP"`, `"ko-KR"`, `"vi-VN"`       |
| `config`                    | Boundaries and school   | See [Config in depth](/en/docs/guide/guides/config); omit for the iztro defaults |

<Callout title="The chart language defaults to zh-CN">
  Omit `language` and you get a Simplified Chinese chart. For English output pass the exact string
  `"en-US"` — every example on the English pages does. The chart language only changes the text of
  names; it never changes which star lands in which palace.
</Callout>

<Callout title="Not a developer? This table is what you hand to your engineers">
  Charting needs only three things: date of birth, hour of birth, gender. Write them out in the
  formats above and hand them over — one call on their side produces the chart. For what the library
  can do and how it is typically used, see
  [Using it without writing code](/en/docs/guide/guides/for-non-developers).
</Callout>

### Hour index [#hour-index]

Zi Wei Dou Shu divides the day into twelve double-hours, and splits the Zi hour into an early and a
late segment — hence 13 index values, 0 through 12.

| Index | Hour           | Time        | Index | Hour          | Time        |
| ----- | -------------- | ----------- | ----- | ------------- | ----------- |
| 0     | Early Zi (Rat) | 00:00–01:00 | 7     | Wei (Goat)    | 13:00–15:00 |
| 1     | Chou (Ox)      | 01:00–03:00 | 8     | Shen (Monkey) | 15:00–17:00 |
| 2     | Yin (Tiger)    | 03:00–05:00 | 9     | You (Rooster) | 17:00–19:00 |
| 3     | Mao (Rabbit)   | 05:00–07:00 | 10    | Xu (Dog)      | 19:00–21:00 |
| 4     | Chen (Dragon)  | 07:00–09:00 | 11    | Hai (Pig)     | 21:00–23:00 |
| 5     | Si (Snake)     | 09:00–11:00 | 12    | Late Zi (Rat) | 23:00–24:00 |
| 6     | Woo (Horse)    | 11:00–13:00 |       |               |             |

<Callout type="warn" title="The late Zi hour is not a typo">
  Someone born between 23:00 and 24:00 uses index `12`, not `0`. The two indexes produce different
  charts: under the default configuration the late Zi hour takes its day pillar from the **following**
  day, while the early Zi hour takes it from the current day. The behaviour is controlled by the
  `day_divide` switch — see
  [Config in depth](/en/docs/guide/guides/config#late-zi-hour-attribution-day_divide).
</Callout>

### About `fix_leap` [#about-fix_leap]

A leap month in the lunar calendar has no month pillar of its own, so charting has to decide whether
its days count towards the preceding or the following month. With `fix_leap = true` (the default)
iztro's correction applies: the first half of the leap month counts as the current month, the second
half as the next. Set it to `false` and the whole leap month counts as the current month.

Only people born in a leap month are affected; otherwise the parameter does nothing.

## Pick a programming language [#pick-a-programming-language]

<Cards>
  <Card title="Rust" href="/en/docs/guide/getting-started/rust" description="cargo add x-iztro" />

  <Card title="Python" href="/en/docs/guide/getting-started/python" description="pip install x-iztro" />

  <Card title="Go" href="/en/docs/guide/getting-started/go" description="go get .../go/iztro" />
</Cards>

## Input validation [#input-validation]

<small>
  For developers
</small>

Dates and hour indexes are validated up front in the **core**, so all three programming languages
sit behind the same line of defence. Invalid input never panics; it is reported the way each
language expects:

| Programming language | Behaviour                                                              |
| -------------------- | ---------------------------------------------------------------------- |
| Rust                 | Returns `Err(IztroError)`; `.code()` gives a machine-readable category |
| Python               | Raises `IztroError` (a subclass of `ValueError`) with the same `.code` |
| Go                   | Returns `*iztro.Error`, matchable against sentinels with `errors.Is`   |
| C FFI                | Returns `{"error":"...","code":"..."}` as JSON                         |

The core validates date format and real existence, the Gregorian range 1583–9999, and hour index
0–12. Gender, chart language and configuration switches — the parameters passed as strings — are
validated in the **binding layer** as they are parsed; in Rust they are enums to begin with, so
there is no invalid value to reject.

See [Error handling](/en/docs/guide/guides/errors).