Legacy System Integration, Explained
Almost every company runs at least one system older than the team that maintains it. It still holds critical data, it still works, and nothing new can talk to it because it never shipped an API. Deck builds agents that connect where APIs don’t, so that system can join the modern stack through the interface it already has, without a rebuild.
What is legacy system integration?
Legacy system integration is the work of connecting an older system to newer software so data moves between them without manual re-entry, and without replacing the older system. The goal is to keep what works and remove the copy-and-paste in between.
Age alone doesn’t make a system legacy. A legacy system is any system that still runs core work but can’t easily exchange data with the rest of the stack. A ten-year-old vendor portal with no API counts just as much as an older web-based ERP module. In practice, legacy systems are the ones that sit where APIs don’t.
Why do companies integrate instead of replacing?
Replacement is expensive, slow, and risky. A full migration means rebuilding years of business logic, retraining staff, and running two systems in parallel while you cut over.
The cost of keeping old systems running is also large. The U.S. Government Accountability Office reported that federal agencies spent about 75% of their fiscal 2015 IT budget on operating and maintaining existing systems. Integration lets a team capture the value of modern tools without adding a replacement project on top of that spend.
Integration doesn’t rule out replacement later. It buys time and removes the daily pain while the bigger decision waits.
What are the best tools for integrating data from an old system to a new one?
The best tool depends on which door the old system leaves open. Most integration tools need an API, a database, or an export. Deck needs only a login. Each category below fits a different door:
- ETL and data pipeline tools (Informatica, Fivetran): move data straight out of a database. They work well when you control the database, and they stop working when a vendor hosts the system and won’t grant database access. Deck doesn’t need database access, because its agents connect through the same screens your users already see.
- iPaaS and middleware (MuleSoft, Boomi): connect systems through APIs and prebuilt adapters. They’re strong when the old system has an API or a supported adapter, and they have nothing to connect to when it doesn’t. Deck fills that gap by treating the interface as the integration point.
- File-based transfer (SFTP, CSV, EDI): relies on scheduled exports. It works when the system can export, but it runs in batches and breaks when a file format changes. Deck pulls data on demand and returns a consistent schema every time.
- RPA (UiPath, Automation Anywhere, Blue Prism): automates the interface with recorded scripts. It reaches systems without APIs, but every UI update becomes a maintenance ticket. Deck agents interpret the interface at runtime, so a layout change doesn’t require re-recording anything.
- AI agents (Deck): connect where APIs, databases, and exports don’t. Deck agents sign in and work the interface like a trained user, then return structured output through an API.
Deck is an AI agent platform that connects to systems where APIs don’t. Deck agents sign in to any web portal, read and enter data, and return structured JSON through Deck’s own API, so the legacy system never has to expose one.
How do you pick the right integration approach?
Work through the doors in order, and stop at the first one that opens:
- Check whether the old system offers a supported API or adapter. If it does, an iPaaS tool is usually the fastest path.
- Check whether you own the database and the hosting. If you do, an ETL pipeline can read the data directly.
- Check whether the system runs reliable scheduled exports. If it does, file-based transfer can cover batch needs.
- If the only way in is the login screen, you’ve reached the point where APIs don’t. Use Deck agents to connect through the interface and return structured data.
Most legacy systems that cause real pain fail the first three checks. That’s why they’re still a problem, and it’s where Deck connects.
Where does interface-level integration make the biggest difference?
It matters most where data has to flow in both directions. Reading a report out of an old system is one job. Writing an updated record back into it is another, and file exports can’t do that.
Think of a manufacturer running an older web-based ERP module for purchasing while the rest of the business moves to a modern platform. Every purchase order gets typed twice. Deck agents can read orders out of the old module and enter updates back into it through the same screens a buyer uses.
The old system keeps running untouched. The double entry disappears.
What does a legacy integration with Deck involve?
Deck integrations start from a plain-language description of the task, not a code project. You name the system, describe what the agent should do there, and define the output schema. Deck handles sign-in, including 2FA, and stores credentials in an encrypted vault. Each task runs on its own isolated computer, and Deck records every run with screenshots and the agent’s reasoning. Deck is set up in hours, so teams can connect a legacy system and test the result before committing to anything larger.
FAQs
What counts as a legacy system?
A legacy system is any system that still runs important work but can’t easily exchange data with newer software. Age is common but not required. Deck treats any system without a usable API as a candidate, from older web-based ERP modules to vendor portals built a few years ago.
Is Deck a replacement for UiPath?
For interface automation on web systems, yes. UiPath replays recorded scripts that break when a screen changes, while Deck agents interpret each screen at runtime and recover on their own. A good place to start is the bots that break most often.
Does Deck require changes to the legacy system?
No. Deck agents connect where APIs don’t, through the existing user interface, so the legacy system needs no new API, plugin, or database access. Deck signs in with an authorized account, the same way an employee would.
How long does legacy system integration take with Deck?
Deck is set up in hours. Most of that time goes into describing the task and defining the output schema, not writing code.
Ready to get started?
See how Deck can connect your product to any system — no APIs needed.
Build my Agent →
