# What is an EDI guide?
Source: https://www.stedi.com/docs/edi-platform/guides/what-is-a-stedi-guide

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## title: What is an EDI guide?

You and your trading partner must agree on the exact format for each transaction type you plan to exchange. In practice, the larger trading partner typically dictates a format that the other trading partner must follow.

These requirements are defined in what the EDI industry calls an **implementation guide**, also known as a companion guide, EDI reference guide, or just a guide. An implementation guide is similar to a Schema definition, with a few peculiarities specific to EDI.

You need an implementation guide for each transaction type you plan to exchange with your partners. For example, you need an implementation guide for an 834 benefit enrollment and a separate guide for an 835 Electronic Remittance Advice (ERA).

## Validation

Implementation guides include information like expected fields, data types and sizes, and which fields are required. You can use these details to validate incoming and outgoing EDI documents.

## Stedi guides vs. standard guides

Standard EDI implementation guides are typically captured in a static format, like PDF, CSV, or even Word document files. In contrast, Stedi guides display EDI requirements as interactive web pages with built-in validation.

Stedi guides are also machine-readable, so Stedi can use them to read and write EDI documents according to each partner's EDI requirements. This is why we recommend always selecting a guide for each [transaction setting](/edi-platform/configure/trading-partners/transaction-settings) in your integration. When you attach a guide, Stedi uses it to validate and translate (inbound) or generate (outbound) the EDI transactions of that type.

Stedi has hundreds of Stedi guides for [X12 HIPAA transactions](https://www.stedi.com/edi/network/hipaa) and [popular retail and logistics trading partners](https://www.stedi.com/edi/network) that you can import into your Stedi account and use in your integration for free.

## Base specifications

All EDI implementation guides are customized versions of a base specification.

There are several EDI standards that provide base specifications. The most common are X12 and EDIFACT. The [EDI Reference](https://www.stedi.com/edi) documentation contains a full list of base specifications for each standard.

* [X12 transaction sets](https://www.stedi.com/edi/x12)
* [EDIFACT messages](https://www.stedi.com/edi/edifact)

A base specification is designed by a standard body to cover all possible use cases for a given transaction. For example, the base specification for ship notices contains fields for every type of ship notice you could ever encounter.

### X12 HIPAA in healthcare

In healthcare, HIPAA covered entities including most payers and providers are legally required to follow the CMS [adopted standard](https://www.cms.gov/priorities/key-initiatives/burden-reduction/administrative-simplification/hipaa/adopted-standards-operating-rules) X12 HIPAA implementation guides when creating transactions. X12 HIPAA is a narrower subset of the X12 standard. The official term for these specifications is a Technical Report Type 3 (TR3), but they are more commonly called X12 HIPAA implementation guides.

These official [X12 HIPAA implementation guides](https://www.stedi.com/edi/network/hipaa) are the ones you want to import into your Stedi account and use in your integration.

Many payers create companion guides for each transaction type, which act as an addendum to the X12 HIPAA implementation guides. For example, [Cigna](https://www.cigna.com/static/www-cigna-com/docs/5010-270-271-companion-guide.pdf), [Centers for Medicare and Medicaid Services](https://www.cms.gov/files/document/current-hets-270/271-companion-guide.pdf), and [UnitedHealthcare](https://www.uhcprovider.com/content/dam/provider/docs/public/resources/edi/EDI-270-271-Companion-Guide-005010X279A1.pdf) all have companion guides for 270/271 Eligibility/Benefit Inquiry and Response transactions (eligibility checks).

Companion guides help you understand the nuances of how each payer implements the X12 HIPAA standard. For example, a companion guide may specify how the payer indicates that a patient has a zero deductible for certain services.

### Implementation guides in logistics and retail

In the logistics and retail world, the existing base specifications for transactions like purchase orders and ship notices are far too generic for day-to-day use. Instead, you and your trading partner must agree on what that transaction set should contain and then adjust the base specification accordingly. The result is an implementation guide, which contains only a subset of [segments](https://www.stedi.com/docs/edi-platform/edi-essentials/x12/segments/what-is-a-segment) from the base specification.

Implementation guides can have other differences from the base specification as well. For example, some segments that are optional in the base specification may be marked as mandatory in the implementation guide.

Each trading partner has their own implementation guide for each type of transaction. For example, [Home Depot](https://portal.stedi.com/app/guides/view/home-depot/purchase-order/01H66G46HEFTS5NSV52VK41NZ2), [Walmart](https://portal.stedi.com/app/guides/view/walmart-edi/4010-purchase-order-acknowledgment/01GNZA51CHFJJD9Y75GSSCXHHW), and [JCPenney](https://portal.stedi.com/app/guides/view/jcpenney/purchase-order-acknowledgment-retail-fulfillment/01GV5KNNM3GAZHCEH5ZZ84XKTQ) all have separate implementation guides for the X12 850 Purchase Order.

These partner-specific implementation guides are the ones you want to import into your Stedi account and use in your integration.