> ## Documentation Index
> Fetch the complete documentation index at: https://gobl-cli-install-gobl-dev.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Header

Header defines the metadata of the body.

## Schema ID

`https://gobl.org/draft-0/head/header`

## Properties

| Title | Property | Type | Description |
| - | - | - | - |
| UUID | `uuid` | string | Unique UUIDv1 identifier for the envelope. |
| Digest | `dig` | [dsig.Digest](/draft-0/dsig/digest) | Digest of the canonical JSON body. |
| Stamps | `stamps` | array of [head.Stamp](/draft-0/head/stamp) | Seals of approval from other organisations that can only be added to non-draft envelopes. |
| Links | `links` | array of [head.Link](/draft-0/head/link) | Links provide URLs to other resources that are related to this envelope and unlike stamps can be added even in the draft state. |
| Tags | `tags` | array of string | Set of labels that describe but have no influence on the data. |
| Meta | `meta` | [cbc.Meta](/draft-0/cbc/meta) | Additional semi-structured information about this envelope. |
| Notes | `notes` | string | Any information that may be relevant to other humans about this envelope |
| From | `from` | [cbc.URI](/draft-0/cbc/u_r_i) | From is the URI-form transport address of the envelope's issuer, e.g. "gobl:invoices.example.com" or "iso6523-actorid-upis::9920:b123123123". |
| To | `to` | [cbc.URI](/draft-0/cbc/u_r_i) | To is the URI-form transport address of the envelope's intended receiver. |
| Ignore | `ignore` | array of string | Ignore lists fully-qualified validation fault codes to suppress when validating this envelope, e.g. "GOBL-EU-EN16931-ORG-ITEM-01". Intended for format-conversion cases where a specific, known fault is acceptable. Covered by the envelope signature when sealed. NOTE: any code may be listed, including structural envelope/header codes — use deliberately. |

## Validation Rules

| Field | Test | Validation Code / Message |
| - | - | - |
| `uuid` | <ul class="gobl-test"><li class="gobl-test-present">Present</li><li>Has timestamp</li></ul> | `GOBL-HEAD-HEADER-01`<br />Header must contain a UUID v1 or v7 with timestamp |
| `dig` | <ul class="gobl-test"><li class="gobl-test-present">Present</li></ul> | `GOBL-HEAD-HEADER-02`<br />Header must have a digest |
| `stamps` | <ul class="gobl-test"><li>No duplicate stamps</li></ul> | `GOBL-HEAD-HEADER-03`<br />Duplicate stamp providers are not allowed |
| `links` | <ul class="gobl-test"><li>No duplicate links</li></ul> | `GOBL-HEAD-HEADER-04`<br />Duplicate link keys are not allowed |


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