# Quality Indicators

> Reference guide to Egon quality indicators: how each code shows whether an input value was validated, corrected, rejected, or approximated.

Quality indicators describe how Egon validated, changed, rejected, or approximated an input value during postal standardization and data validation services.

## How to Read an Indicator

Each quality result in an API response contains three key elements:

| Field         | Type     | Description                                                                                |
| ------------- | -------- | ------------------------------------------------------------------------------------------ |
| `flag`        | `String` | High-level validation status indicating whether data was unchanged, corrected, or rejected |
| `code`        | `Number` | Granular error or quality rule code specifying the exact operation performed               |
| `description` | `String` | Human-readable explanation of the validation outcome                                       |

## Flag Values

The high-level `flag` summarizes the overall validation outcome:

| Flag                                                                              | Status                        | Meaning                                                                                                                     |
| --------------------------------------------------------------------------------- | ----------------------------- | --------------------------------------------------------------------------------------------------------------------------- |
| 0 · OK           | **Validated without changes** | The input value perfectly matched reference authority databases and required no alterations.                                |
| 1 · Changed      | **Validated with changes**    | The input value was recognized and corrected, completed, or standardized according to official postal rules.                |
| 2/3 · Not valid | **Not validated**             | The value could not be validated due to ambiguity, syntax errors, missing mandatory elements, or no matching records found. |

## Indicator Catalogs

- [Address Indicators](https://documentation.egon.com/docs/quality-indicators/address.md): Detailed quality codes for locality, street name, postal code, and house-number validation. (201 codes)
- [Birth Indicators](https://documentation.egon.com/docs/quality-indicators/birth.md): Quality indicators returned for birth-date coherence and birthplace validation. (8 codes)
- [Email Indicators](https://documentation.egon.com/docs/quality-indicators/email.md): Syntax validation, domain verification, certified PEC identification, and disposable email detection. (32 codes)
- [Geocoding Indicators](https://documentation.egon.com/docs/quality-indicators/geocoding.md): Coordinate sources (TomTom, HERE, Egon, cadastre) and spatial precision approximation levels. (88 codes)
- [Person & Name Indicators](https://documentation.egon.com/docs/quality-indicators/person.md): Name and surname parsing, academic title detection, corporate legal forms, and gender consistency. (46 codes)
- [Phone Indicators](https://documentation.egon.com/docs/quality-indicators/phone.md): Telephone number standardization, international prefix addition, and geographical area code checks. (25 codes)
- [Tax Code Indicators](https://documentation.egon.com/docs/quality-indicators/tax-code.md): Italian fiscal code calculation, checksum verification, omocody resolution, and identity checks. (59 codes)
- [VAT Indicators](https://documentation.egon.com/docs/quality-indicators/vat.md): VAT number syntax validation, European VIES cross-checks, and corporate registry verification. (59 codes)

## Also in Reference

Complementary reference guide and data dictionary:

- [Domains & Dictionaries](https://documentation.egon.com/docs/domains.md): Standardized domain codes used in request and response fields (administrative codes, person types, phone lines).