IDS Connect: linking trade software to the wholesale shop

The building services wholesale trade lives off the skilled trades. The 54 member companies of DG Haustechnik generate combined annual sales of around 20 billion euros (DG Haustechnik) and are close to around 50,000 trade customers through more than 1,900 branches (DG Haustechnik). On the other side, the German plumbing, heating and air conditioning trade counts about 48,000 businesses with 390,000 employees and sector sales of around 59.1 billion euros in 2025 (ZVSHK). Between them sits a range nobody can keep in their head: more than nine million articles are accessible, more than 40,000 of them held in stock per location on average (DG Haustechnik). How volumes like these get into a shop in the first place is covered in our article on bulk import via the sync API.

For the trade business, the need arises in one place: the trade software in which it writes quotes, orders and invoices. In a representative 2025 survey of 504 trade businesses with at least one employee, 68 percent said they send quotes digitally, and 62 percent send their invoices digitally (Bitkom). The same survey names high material costs as a challenge for 59 percent of businesses, and 75 percent report a shortage of skilled workers (Bitkom). Anyone pricing a quote under these conditions needs current purchase prices without detours and has no time to copy article numbers from one window into another.

The specification states the benefit for both sides in plain terms. For trade software, it matters that all wholesalers' web shops can be addressed in an identical way, and the wholesaler can exchange data with many customers using standard software (IDS interface specification). So that trade software can find a shop at all, there are the directory services SHK Connect and Open Connect. They list addresses and versions of the interfaces offered, and wholesalers should register their interfaces there (ITEK). A shop without IDS access and without a directory entry cannot be reached from trade software, even if it works well in the browser. How we support wholesalers across the entire integration is described on our page on ERP integration for wholesale.

Every call starts with an automatic login. The trade software opens the shop in a browser window and transfers customer number, user name and password in the parameters kndnr, name_kunde and pw_kunde, each with up to 50 characters (IDS interface specification). These are the credentials the customer already uses in the shop. The transfer uses POST with the form type multipart/form-data; the standard does not support the GET variant because its parameter length is insufficient. The request also carries the hook URL, the trade software's return address, with up to 256 characters (IDS interface specification).

For the shop this means: it needs its own entry point that accepts POST requests from outside, checks the credentials against the customer account, opens a session and keeps the call parameters for the entire process. If the login fails, the shop shows the error in the browser window. If it allows a manual login, the parameters from the trade software must be preserved so that the process can still find its way back (IDS interface specification). For business customers with several employees in the shop, the mapping matters: customer number and user name must point to exactly the account whose prices, delivery addresses and approvals apply. How to secure access to interfaces in general is covered in our article on OAuth 2.0 and token security.

Since version 2.5, trade software can call the search in the wholesale shop directly (ITEK). The search term sits in the parameter searchterm, several terms are separated by spaces, and the search runs on the receiving system's own logic, which the call does not influence (IDS interface specification). That sounds like a detail and is the opposite: whatever the shop search does not find, the tradesperson will not find from the software either. Manufacturer numbers, customer part numbers, synonyms from everyday site language and tolerance for typos help decide whether the search gets used. How third-party numbers get into the search index is described in our article on customer part numbers in the B2B shop. The selected items return to the hook URL the same way as with WKE.

The article deep link is the fastest action. The trade software passes the wholesale article number in the parameter ghnummer, and the shop responds with a page showing the article data (IDS interface specification). This function gives direct insight into current prices and the availability of articles (ITEK). This is exactly where it shows whether shop and ERP work together. After the automatic login, customers must see their purchase price, not the list price, and availability must reflect the stock of the warehouse that supplies them. How customer-specific prices reach the shop quickly and consistently is covered in our article on B2B price synchronization, and the basics of stock transfer on our page on inventory system integration.

When the tradesperson orders in the shop, the process does not end with the order confirmation. The specification states that for some trade software it is important that the order also comes back into the trade system. Anyone using order tracking and invoice checking based on it there needs the return without exception (IDS interface specification). For this purpose, the basket carries the order number from the trade software and the order confirmation number from the wholesale system, each with up to 15 characters (IDS interface specification). In the shop, the order is created like any other, handed over to the ERP and additionally reported to the hook URL with the flag for a return with order.

The circle closes at the latest with the invoice. For domestic business-to-business supplies from January 1, 2027, the transitional rule for invoices on paper or in another electronic format applies only if the issuing company's total turnover in the previous year did not exceed 800,000 euros (German VAT Act). Apart from that, only exchange via EDI remains exempt in 2027, and both transitional rules end on December 31, 2027. A wholesaler above that threshold that does not invoice via EDI therefore issues structured e-invoices to its trade customers, except in cases such as small-amount invoices. So that trade software can match an invoice to the order automatically, the tradesperson's order number belongs in the purchase order reference, which the Peppol specification carries under business term BT-13 as the identifier issued by the buyer (OpenPeppol). Whoever takes this number over cleanly in the IDS basket, writes it to the ERP and prints it on the invoice again turns the customer's invoice check into a match instead of a search. More on our e-invoicing page and in our article on whether the invoice comes from the shop or the ERP.

IDS Connect is often mentioned in the same breath as Datanorm and Open Masterdata, but it solves a different task. Datanorm and Open Masterdata supply the trade software with master data. Open Masterdata stands for on-demand supply of product master data and was developed to replace outdated master data processes based on Datanorm; the standard covers all Datanorm use cases, from initial setup to price updates for large numbers of articles (ITEK). IDS Connect, by contrast, takes the user into the shop and brings a basket back. The two complement each other: master data makes sure an article is known in the trade software, IDS Connect makes sure it is ordered at the current price. For procurement systems of industrial customers, OCI is the right route instead.