APIs quietly power the products your customers touch every day, from mobile checkout flows to the data feeds behind your dashboards. A skilled API developer connects your systems, partners, and third-party services so information moves securely and reliably across finance, healthcare, retail, and SaaS. Getting that foundation right early saves you costly rebuilds as you scale.
What does an API developer do?
An API developer builds and maintains the interfaces that let separate applications share data and talk to each other. They translate business needs into endpoints that are fast, well-documented, and safe to expose. It helps to understand what an API is before you write your job post, since the right hire depends on the work you're planning.
Depending on the project, an API developer's responsibilities can include:
- Designing APIs. Creating RESTful and GraphQL endpoints that other applications can call quickly, reliably, and predictably
- Handling authentication and security. Setting up OAuth, API keys, and rate limits so only the right users reach your data
- Building third-party integrations. Connecting payment processors, CRMs, and other external services your product depends on to work
- Writing documentation. Producing clear, current references so your team and outside partners can adopt the API without guesswork
- Managing performance and scalability. Monitoring, caching, and versioning endpoints so they hold up as your traffic and usage grow
How to hire an API developer on Upwork
Once you know what you need, hiring moves quickly. In fact, 89% of first-time clients complete a contract on Upwork. The four steps below walk you through posting, evaluating, interviewing, and starting work with the right API developer.
Step 1: Post a job
Document your API project, the systems it will connect, and the technical requirements so the right developers can evaluate whether they're a good fit.
- Describe your API project, integrations, and the business goals the API will support
- Specify the technologies, protocols, and standards involved, such as REST, GraphQL, OAuth, JSON, or OpenAPI
- Define the deliverables, including endpoints, integrations, documentation, testing, and deployment requirements
- Share your timeline, budget, and any performance, security, or scalability requirements
- Start with a back-end-developer job description template
Use the Job Post Generator, powered by Umaโข, Upwork's Mindful AI, to turn a few plain sentences into a ready-to-edit API developer job post. On Upwork, the average time from job post to first proposal is three hours.
Step 2: Evaluate candidates
Review each candidate for evidence that they've successfully designed, built, and maintained production APIs.
- Examine portfolios for secure, scalable APIs, integrations, and technical documentation
- Confirm experience with the frameworks, cloud platforms, and programming languages your project requires
- Evaluate experience with tools such as Postman, Swagger/OpenAPI, or API testing frameworks
- Read client feedback for communication, code quality, and successful project delivery
Uma can conduct instant video interviews and provide side-by-side candidate comparisons to help you identify the strongest fit.
Step 3: Interview your top choices
Use interviews to understand how candidates design APIs, solve technical challenges, and support long-term maintenance.
- Ask how they design secure, scalable APIs and version them over time
- Discuss their experience with REST, GraphQL, authentication, and third-party integrations
- Explore how they test APIs, troubleshoot issues, and document their work
- Review these back-end developer interview questions and adapt them for your API project
- Consider a small paid API design or integration task before committing to a larger engagement
Conduct interviews through Upwork Messages, where you'll receive transcripts and summaries after each call.
Step 4: Agree on scope and begin work
Once youโve selected your developer, align on deliverables, milestones, and technical requirements so everyone shares the same expectations.
- Define deliverables such as API endpoints, integrations, documentation, test suites, and deployment artifacts
- Set milestones for API design, development, testing, security review, and deployment
- Agree on authentication methods, API credentials, versioning strategy, and ongoing maintenance responsibilities
- Clarify performance requirements, review checkpoints, and acceptance criteria before development begins
Use Upwork's contract workroom and Messages to keep feedback, files, and approvals organized in one place. Identity verification, payment protection, hourly tracking, and project funds help keep the engagement secure and on track.
Upwork is not affiliated with and does not sponsor or endorse any of the tools or services discussed in this article. These tools and services are provided only as potential options, and each reader and company should take the time needed to adequately analyze and determine the tools or services that would best fit their specific needs and situation.
The rates and information provided in this article are based on current data and industry sources available at the time of publication. Freelance rates can vary depending on factors such as experience, location, project scope, and market conditions. Readers are encouraged to conduct their own research to confirm current rates and trends, as this information may change over time.