> ## Documentation Index
> Fetch the complete documentation index at: https://docs.anyformat.ai/llms.txt
> Use this file to discover all available pages before exploring further.
# Fields
> What a field is and the three properties every field has.
A **field** is one piece of information inside a [schema](/concepts/schemas).
Examples:
* Invoice number
* Issue date
* Total amount
* Vendor name
Fields drive data quality. Clear fields give better results and less review.
***
## The three field properties
Every field has at least three properties.
A human-readable label that still makes sense outside anyformat.
Examples: `invoice_number`, `issue_date`, `total_amount`.
Use snake\_case so the name is safe to use as a JSON key or column header.
The kind of value anyformat expects: text, date, number, and others.
The type improves consistency, validation, and output quality. [Field types](/concepts/field-types) has the full list.
Plain-English guidance for how to extract the value.
Example: "Extract the final total including taxes. Ignore subtotals."
[Instructions](/concepts/instructions) shows how to write a good one.
***
## Field source: extraction vs. smart lookup
Every field also has a **source**. It tells anyformat where the value comes from. By default anyformat reads the value off the document. The other source matches the value against a reference file you attach. [Smart Lookup](/guides/nodes/smart-lookup) covers how that works and when to use it.
***
## What's next?
The full list: text, date, number, object, enum, multi-select
Write effective extraction instructions
Enrich extracted values against a reference file
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