IT Glossary
What is OpenAPI?
The standard format for describing an API completely: which addresses it exposes, which parameters it accepts and which responses it returns.
There is a reliable way to predict how long an integration will take, and it has almost nothing to do with the technology involved: ask whether the API has an OpenAPI specification. OpenAPI, known previously as Swagger, is the technical blueprint of an interface — a standardized file describing exactly which endpoints exist, which parameters they accept, and which responses and errors they return. From that single file you can generate interactive documentation, client code in dozens of programming languages, and tests that continuously check whether the API honors its own contract. The practical gap is enormous. An integration against a documented API starts within hours, because the partner reads the specification and generates the connecting code. An integration against an API described through a chain of emails starts with weeks of questions, each of which can only be answered by one person who happens to be on holiday. For a company commissioning an API the rule follows directly: make the OpenAPI specification a mandatory deliverable in the contract. It is your guarantee that future integrations, and any eventual change of supplier, will not begin again from zero.
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Why it matters for your business
Integrations that start in hours, not weeks
Partners receive a complete specification and generate their own connecting code — months of emails asking what format that field uses simply disappear.
Documentation that never lies
Interactive documentation is generated from the same specification the API runs against — no more PDFs sitting three versions behind reality.
A contract verified automatically
Tests continuously compare the API’s real behavior against the specification — any deviation is caught before release, not inside a partner’s production system.
Frequently asked questions
Are OpenAPI and Swagger the same thing?
Practically yes: Swagger was the original name of the specification, donated in 2015 to the foundation that renamed it OpenAPI. Swagger survives as the name of the popular tooling around it — Swagger UI for interactive documentation, Swagger Editor for writing specifications by hand.
Is the OpenAPI specification written by hand?
Both approaches exist. Design-first means the specification is written before the code and the code then follows it, which is ideal when several teams depend on the contract. The alternative generates it automatically from annotations inside the code, which is more comfortable on small projects. What matters is that the specification exists and is treated as the source of truth.
Which version of OpenAPI should I ask for?
OpenAPI 3.x is the current standard, with 3.1 aligning the specification fully with JSON Schema; the older 2.0 still turns up on legacy interfaces. For a new project, ask explicitly for 3.1, since modern tooling supports it completely and nothing is gained by starting a step behind.
Let’s talk about your project
Message us on WhatsApp or send an email — you talk directly to a developer.
office@northdan.com · +40 752 070 247