API projects vary considerably, from a single third-party integration to the backend architecture behind an entire digital product. The providers below cover custom API creation, system integration, microservices, API testing, and ongoing maintenance, with each offering a slightly different delivery model.
1. Gilzor
Gilzor develops the backend systems that support web and mobile products for startups, small and medium-sized businesses, and product studios. Its engineering stack includes Node.js, TypeScript, Python, FastAPI, Django, SQLAlchemy, and microservices, giving the team a practical foundation for custom API development and integration-heavy applications.
The company can handle architecture, implementation, QA, deployment, and continued feature development. Gilzor is particularly relevant when an API forms part of a larger product rather than an isolated technical task. Its experience with AWS, Docker, Kubernetes, PostgreSQL, MongoDB, messaging tools, and API testing through Postman also supports projects that need reliable infrastructure around the interface.
Key Facts
- Best for: Startups and growing product companies
- Core services: API development, backend development, web development, mobile development, QA, technical troubleshooting
- API capabilities: FastAPI, Node.js frameworks, microservices, Postman testing
- Technologies: TypeScript, Python, Node.js, Django, PostgreSQL, MongoDB, AWS
- Location: Warsaw, Poland and Limassol, Cyprus
- Notable strength: Full product engineering around API-based applications
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Contact Information
- Website: www.gilzor.com
- Email: contacts@gilzor.com
- LinkedIn: www.linkedin.com/company/gilzor-softwaredevelopment
- Address: Poland, Warsaw, Office 58, street Adama Mickiewicza 37, 01-625
2. NeoWork
NeoWork takes a staffing-focused approach to API development. Instead of delivering only a fixed-scope project, the company recruits dedicated API developers from the Philippines and Colombia who work as part of the client’s existing engineering team. This arrangement may suit businesses with a continuing integration backlog or products that need regular API maintenance.
Its published capabilities cover RESTful API implementation, GraphQL schemas, microservices, webhooks, API gateways, OAuth 2.0, JWT authentication, rate limiting, caching, and OpenAPI documentation. NeoWork also supports third-party integrations, API versioning, automated testing, and performance optimization. The model is designed for longer engagements where developers need to learn the client’s architecture and development standards.
Key Facts
- Best for: Companies extending an internal development team
- Core services: API developer staffing, software development, IT outsourcing
- API capabilities: REST, GraphQL, webhooks, API gateways, microservices
- Security: OAuth 2.0, JWT, rate limiting, input validation
- Delivery locations: Philippines and Colombia
- Notable strength: Dedicated developers who work within the client’s existing workflow
Contact Information
- Website: www.neowork.com
- Facebook: www.facebook.com/neoworkteam
- LinkedIn: www.linkedin.com/company/neoworkteam
- Instagram: www.instagram.com/neoworkteam
3. A-listware
A-listware provides API-related engineering within broader software development and application integration projects. Its teams work across custom software, enterprise applications, cloud solutions, web applications, legacy modernization, and application maintenance. That range makes the company a reasonable option when API development is tied to a larger modernization or product delivery program.
The available technology stack includes .NET, Java, TypeScript, Python, Go, PHP, Node.js, Ruby, and C++. Clients can use a fully managed outsourcing model or add backend engineers to an existing team. Compared with providers centered exclusively on APIs, A-listware offers a wider mix of development, QA, infrastructure, and support capabilities.
Key Facts
- Best for: Businesses combining API work with custom software development
- Core services: Application integration, custom software, cloud applications, web development
- Technologies: .NET, Java, Python, TypeScript, Go, PHP, Node.js
- Engagement models: Managed development, outsourcing, team augmentation
- Locations: United Kingdom and United States
- Notable strength: Coverage across the full software development lifecycle
Contact Information
- Website: a-listware.com
- Phone: +1 (888) 337 93 73
- Email: info@a-listware.com
- Address: North Bergen, NJ 07047, USA
- LinkedIn: www.linkedin.com/company/a-listware
- Facebook: www.facebook.com/alistware
4. OSKI Solutions
OSKI Solutions explicitly includes custom APIs in its backend development offering. The team builds server-side logic, database layers, web APIs, and microservices, with attention to performance, security, and future scalability. Its backend technology options include C# and .NET, Node.js, Python, and PHP.
The company also provides system integration, cloud and DevOps support, QA, maintenance, and security services. This combination can be useful for organizations that need more than endpoint development, particularly when the work involves connecting APIs to cloud infrastructure or existing business systems. OSKI serves projects across fintech, healthcare, insurance, education, logistics, travel, and e-commerce.
Key Facts
- Best for: Custom backend systems and integration-heavy applications
- Core services: Custom APIs, backend development, system integration, cloud and DevOps
- Technologies: C#, .NET, Node.js, Python, PHP
- Industries: Fintech, healthcare, insurance, logistics, education, e-commerce
- Notable strength: API development combined with deployment and ongoing backend support
Contact Information
- Website: oski.site
- Phone: +48571282759
- Email: contact@oski.site
- Address: Kaupmehe tn 7-120, Tallinn, 10114, Estonia
- LinkedIn: www.linkedin.com/company/oski-solutions
5. Itexus
Itexus concentrates on API development and integration for fintech and financial services. Its work includes connections to banks, payment gateways, open banking platforms, KYC and AML providers, credit bureaus, brokers, exchanges, market data feeds, and legacy core banking systems.
The team handles API contract design, data mapping, authentication, sandbox testing, fallback logic, monitoring, and production rollout planning. Backend technologies include Java, .NET, TypeScript, and Python, while Kafka and RabbitMQ support asynchronous workflows and data exchange. Itexus is therefore better aligned with regulated, integration-heavy financial products than with a straightforward public API for a small standalone application.
Key Facts
- Best for: Fintech platforms and regulated financial systems
- Core services: API integration, fintech software, legacy modernization, QA, DevOps
- API capabilities: Open banking, payment, KYC, broker, exchange, and market data integrations
- Technologies: Java, .NET, TypeScript, Python, Kafka, RabbitMQ
- Locations: United States and Poland
- Notable strength: Financial domain knowledge for complex API ecosystems
Contact Information
- Website: itexus.com
- Email: info@itexus.com
- Address: 8, The Green, STE road, Dover, DE 19901, United States
- LinkedIn: www.linkedin.com/company/itexus
- Facebook: www.facebook.com/itexus
- Twitter: x.com/ItexusSoft
- Instagram: www.instagram.com/itexus.soft
6. Lengreo
Lengreo offers API creation as part of its custom web development service. The company assembles full project teams that can include full-stack developers, business analysts, designers, project managers, QA engineers, and DevOps specialists. Its technical focus includes Node.js, React, Laravel, Ruby on Rails, TypeScript, and Next.js.
This provider may appeal to businesses that need an API alongside a customer-facing web platform, product design, and launch support. LenGreo also brings digital marketing capabilities into the same organization, which is unusual among the companies in this list. For a purely backend assignment, a more technically specialized provider may be preferable, but LenGreo offers useful breadth for end-to-end web products.
Key Facts
- Best for: API-backed web products requiring design and launch support
- Core services: API creation, custom web applications, cloud-native systems, QA
- Technologies: Node.js, React, Laravel, Ruby on Rails, TypeScript, Next.js
- Locations: Amsterdam, Netherlands and Kyiv, Ukraine
- Notable strength: Combined product development and digital marketing capabilities
Contact Information
- Website: lengreo.com
- E-mail: hi@lengreo.com
- Twitter: x.com/Lengreo
- LinkedIn: www.linkedin.com/company/lengreo
- Instagram: www.instagram.com/lengreo.agency
- Address: Vrijstraat 9 C/D, 5611 AT Eindhoven, Netherlands
- Phone: +31 686 147 566
7. 21Century.Tech
21Century.Tech handles API integrations within full-stack software projects, including MVPs, new product features, legacy refactoring, and connections to third-party services. Its approach pairs senior engineers with AI-assisted development tools, while architecture decisions, security checks, code reviews, and final quality remain under human control.
This model is geared toward businesses that want to move quickly without separating API work from the rest of the product. The company can take an initial specification or design, build the required backend connection, add tests and documentation, and deploy the finished feature to the client’s infrastructure or its own environment.
Key Facts
- Best for: Fast-moving startups and product teams
- Core services: Full-stack development, MVPs, legacy refactoring, third-party integrations
- API capabilities: Backend connections and external service integrations
- Delivery approach: AI-assisted development with senior engineer oversight
- Location: Miami, United States, with a remote-first model
- Notable strength: Short delivery cycles for defined software features
Contact Information
- Website: 21century.tech
- Email: kirill@oski.site
8. Mobian Studio
Mobian Studio provides API engineering as part of end-to-end product development. Its teams cover mobile applications, enterprise backends, cloud infrastructure, QA, and integration with existing systems. Businesses can outsource an entire project or add Mobian engineers directly to an internal team.
The company’s domain experience includes healthcare, fintech, logistics, and enterprise IT. That background is useful for APIs connected to payment workflows, healthcare data standards such as HL7 and FHIR, or operational platforms with complicated legacy dependencies. Mobian also offers post-launch monitoring, scaling support, and continued development, so the same engineers can maintain the interfaces after release.
Key Facts
- Best for: API-backed mobile and enterprise products
- Core services: Backend development, APIs, mobile apps, cloud infrastructure, QA
- API capabilities: Legacy integration, healthcare data connections, payment workflows
- Engagement models: Project outsourcing and engineering team augmentation
- Location: Tallinn, Estonia
- Notable strength: API delivery within complete mobile and software products
Contact Information
- Website: mobian.studio
- Email: info@mobian.studio
- Address: Harju maakond, Tallinn, Kesklinna Linnaosa, Masina tn 22, 10113
- LinkedIn: www.linkedin.com/company/mobian-studio
9. net-devs
net-devs develops enterprise software across .NET, JVM, Node.js, Python, and Go, all common choices for API servers and integration layers. Its stack-independent approach is useful for projects where the provider must work around an established architecture instead of pushing one preferred framework.
The company combines enterprise development with cloud and platform engineering on Azure, AWS, and Google Cloud. This allows its teams to handle not only application logic but also deployment, infrastructure, testing, and continued iteration. Senior engineers supervise delivery and retain responsibility for architecture and final quality, while AI tools assist with drafting code, tests, and documentation.
Key Facts
- Best for: Enterprise APIs and cloud-based backend systems
- Core services: Enterprise development, cloud engineering, AI engineering, modernization
- Technologies: .NET, JVM, Node.js, Python, Go
- Cloud platforms: Azure, AWS, Google Cloud
- Location: Warsaw, Poland
- Notable strength: Senior-led engineering across multiple backend stacks
Contact Information
- Website: net-devs.com
- Phone: +48 571 282 759
- Email: contact@net-devs.com
- Address: Obrzeżna 1D, 02-691 Warszawa
- LinkedIn: www.linkedin.com/company/net-devs
10. SoftPro
SoftPro builds custom software using Node.js, C# and .NET, Python, PHP, and the broader Microsoft technology stack. Its backend development work supports scalable business applications, while its cloud practice covers Azure, AWS, cloud-native software, migration, and infrastructure management.
A published CRM and HRM project includes a RESTful API built with ASP.NET Web API to connect the platform’s frontend and backend. This practical experience makes SoftPro relevant to companies developing APIs for internal portals, workflow automation, SaaS products, and enterprise management systems. The company also provides full-stack development and ongoing maintenance after the initial release.
Key Facts
- Best for: Business platforms built around Microsoft technologies
- Core services: Backend development, custom software, web applications, cloud development
- API capabilities: RESTful APIs and integration with existing business systems
- Technologies: ASP.NET, .NET Core, C#, Node.js, Python, PHP
- Location: Warsaw, Poland
- Notable strength: API development for CRM, HRM, and enterprise applications
Contact Information
- Website: soft-pro.pl
- Address: Poland, Warsaw, Mazowieckie Voivodeship, 13 Erasmus Ciołka St. 401
Conclusion
The right API development partner depends less on who has the longest service list and more on what the API actually needs to do. Gilzor and OSKI Solutions are well suited to API work tied to a larger digital product, while Itexus brings deeper experience with financial platforms and regulated integrations. NeoWork offers a different route through dedicated offshore developers, and A-listware can support broader software programs where APIs are only one piece of the system.
LenGreo may make more sense for companies building a complete web product that also needs design and launch support. Before settling on any provider, share the current architecture, expected traffic, security requirements, documentation standards, and long-term maintenance plans. A well-built API can quietly keep a product running for years. A rushed one has a habit of becoming everyone’s problem later.
