Choosing a software development partner should start with the problem, not the technology. If an agency is recommending a framework, architecture or platform before it properly understands what you’re trying to achieve, that’s worth questioning.
Relevant technical experience
Look for evidence that the agency has solved problems resembling yours rather than simply checking whether a particular framework appears somewhere on its services page. If you already have a substantial Ruby on Rails application, genuine Rails experience matters; the same applies to Laravel, Python and Salesforce.
If you’re starting from scratch, broader experience may be more valuable. In that situation you want a team capable of deciding what should be built before deciding how to build it.
Software engineering maturity
Good software needs to survive beyond launch, so ask how an agency approaches architecture, source control, code review, automated testing, CI/CD, staging environments, infrastructure, monitoring, documentation and security.
You don’t necessarily need to understand every technical detail or dictate the engineering process yourself. What you’re looking for is evidence that there is a considered process behind the work and that decisions are being made with the long-term health of the software in mind.
APIs and integrations
Business software rarely operates alone. CRMs, ERPs, payment providers, identity platforms, accounting systems, marketing tools and internal databases often need to exchange information reliably, which means experience with custom APIs and systems integrations can be every bit as important as experience building the application itself.
An impressive interface isn’t much use if somebody still has to copy the resulting information into three other systems manually.
Ownership and maintainability
Make sure you understand who owns the source code, where it’s hosted and what happens if you eventually move to another development partner. Good software shouldn’t be deliberately mysterious, and a competent agency should be comfortable producing maintainable code that another capable development team could understand and continue working on.
Long-term support
Launching software is normally the beginning rather than the end of the relationship. Requirements change, dependencies need updating, users find unexpected ways to use things, new integrations become necessary and security requirements evolve.
Look for a development partner capable of supporting, monitoring and improving what it builds over time rather than treating deployment as the point at which its responsibility ends.