Look first at proven experience, not the size of the portfolio. Ask for a couple of projects that resemble your technology stack, offshore software development and then ask specifically which engineers actually built it. A serious vendor is happy to connect you with the tech lead. Vague answers at this stage generally mean the demo work came from somewhere else.
The agreement warrants more attention than the sales deck. Three clauses do most of the work: ownership of the code, kotlin development agency non-disclosure, and exit terms and handover. All the work product should transfer to you once invoices are settled, along with designs, scripts and infrastructure configuration. Look closely at wording that leaves reusable components with the vendor, docker software development company because this is frequently the part you cannot replace later.
Ask where their numbers come from. A credible estimate is accompanied by a written set of assumptions, a breakdown by feature or module and a range rather than a single number. A fixed-price contract is only reasonable when the scope is genuinely frozen; when the scope is still moving the vendor prices the risk in and you fund the buffer regardless. Time and materials shifts that risk to you, so it needs visible weekly reporting and php portal development a spending cap.
Process matters more than team size. Establish what happens when the scope changes, who signs off on a feature and how testing is organised. A mature team will be able to walk you through a working build every one or two weeks. Acceptance criteria in writing are the only reliable protection against the it-was-never-in-scope conversation.
Before signing, think about the handover while the relationship is still good. Ask that the repository stays on infrastructure you own from the first commit, and that a readme and architecture notes are kept current as the code changes. A provider confident in its own work will agree quickly; a long negotiation over it says most of what you need to know.