How to choose a software house when you need to connect existing systems

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Who this guide is for

This guide is for business owners and IT managers who need to choose a software house for a very specific job: connecting systems that already exist. Typical examples are an ERP, CRM, ecommerce platform, warehouse tool, or customer portal that must exchange data without manual re-entry.

The question is not only who can build software, but who can design an integration that stays stable when one system changes.

Why this choice is different from a normal software project

In an integration project, the real product is not just code. It is a contract between systems.

Microsoft describes APIs as a contract between services and stresses semantics, versioning, and backward compatibility when systems evolve (Microsoft Learn). Google Cloud makes a similar point: an API can remain consistent even if the backend changes, as long as the public contract stays stable (Google Cloud).

For a buyer, the practical takeaway is simple: a capable software house should be able to explain how it will preserve that contract over time, not only how it will deliver the first release.

What to prepare before asking for quotes

A good integration project starts with a clear brief. Before you contact vendors, prepare four things:

  1. List the systems involved
    Example: ecommerce platform, ERP, CRM, warehouse tool.

  2. Describe the exact workflow
    What data is created, what is updated, who owns each step, and which system is the source of truth.

  3. Mark business rules and exceptions
    Which fields are mandatory, which statuses are valid, and when a human must review the case.

  4. State operational constraints
    Volume, timing, sensitive data, third-party dependencies, and any security or compliance limits.

Without these inputs, vendors often respond with generic proposals that sound plausible but are hard to validate.

Questions that separate a capable vendor from a weak one

1) Can they restate the integration as a contract?

Ask the vendor to explain the project back to you in contract terms: which systems communicate, which data is exchanged, which fields are required, and which errors can occur. If they cannot express the integration clearly, the project is not yet well framed.

2) Do they document the interface in a way someone else can maintain?

Good documentation should include fields, statuses, response codes, dependencies, and version notes. If the original team disappears, another team should still be able to understand how the connector works.

3) How do they handle versioning and compatibility?

APIs change. The real question is how changes are managed. Ask how they handle breaking changes, how long older versions remain supported, and who decides when a change is not backward compatible. Microsoft’s guidance on API design is explicit that versioning and stable semantics are central to avoiding failures as services evolve (Microsoft Learn).

4) What happens on timeout, retry, or partial failure?

This is where many integrations fail in practice. Ask what happens if a request succeeds on one side but the response is lost, or if the same operation is retried. The answer should cover retries, duplicate prevention, reconciliation, and logging, not just “we handle exceptions.”

5) How is the end-to-end flow tested?

Testing the endpoint alone is not enough. The vendor should verify the full path: input data, transformation rules, target system update, and business validation. You want proof that the process works in the real workflow, not only in a technical demo.

6) Who owns maintenance after go-live?

The connector is not finished at launch. Ask who monitors it, who fixes it when a third-party system changes, and what support process exists after delivery. If maintenance is vague, the project is more fragile than it looks.

Warning signs that should slow you down

Be cautious if the vendor:

  • talks only about speed and not about contract, versioning, or maintenance;
  • cannot describe how they handle edge cases;
  • offers a demo but no maintenance plan;
  • avoids discussing retries, partial failures, or duplicate records;
  • does not produce documentation usable by a different team later.

These are not proof of failure, but they are strong indicators that the project may depend too much on the people who built it and too little on a repeatable method.

A concrete example of a process worth replacing

A common manual workflow looks like this: an order arrives in ecommerce, an operator copies customer data into the ERP, checks payment status, updates stock, and re-enters the shipping address. Each handoff creates a risk of delay or error.

A capable software house should be able to translate that into an integration brief such as:

  • system A: ecommerce platform;
  • system B: ERP;
  • data to sync: order ID, customer details, shipping address, totals, payment status;
  • exceptions: duplicate customer, missing address, unpaid order;
  • goal: remove routine re-entry and leave only exceptions for human review.

The expected output is not just “automation.” It should be a connector that creates traceable records, logs each attempt, blocks invalid data, and makes exceptional cases easy to review.

Acceptance checks before you approve the project

Before sign-off, verify that:

  • data reaches the right target system;
  • errors are readable by the person who must resolve them;
  • retries do not create duplicates;
  • backend changes do not silently break the external contract;
  • someone is explicitly responsible for maintenance after delivery.

Google Cloud notes that a backend can evolve without changing the public API if the contract stays coherent (Google Cloud). That is a useful buying criterion too: you are not just purchasing a first release, but a connection that can survive real operational change.

The first question to ask in the call

A strong opening question is:

“How do you design the integration so it remains stable when one of the connected systems changes version or behavior?”

If the answer mentions contract, documentation, versioning, testing, and maintenance, you are likely speaking with a vendor who understands the real problem. If the answer stays at the level of tools and speed, you probably need more detail before deciding.

If your case is similar, the next step is to map the process you want to automate: the systems involved, the data that moves between them, and the points where people still intervene manually.

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