18 Best Third-Party API Integration Companies in the USA (2026)

Gilzor is a software development company that works with startups, SMBs, and product teams on web, mobile, and custom software projects. As part of our development process, we build and connect third-party API integrations that help products exchange data with payment systems, cloud platforms, communication tools, business software, and other external services. We provide software development and API integration services for companies in different markets, including the USA, where connected digital products often rely on multiple external platforms.

We approach API integration as part of a broader product architecture rather than as a standalone task. Before implementation, we analyze business requirements, define the right integration approach, and make sure connected systems work reliably together. Alongside development, we handle testing, ongoing maintenance, and product updates so integrations continue to support changing business needs over time.

Apriorit focuses on API development and third-party API integration as part of custom software engineering projects. Their team connects web, desktop, mobile, and cloud applications with external platforms, making it easier for businesses to exchange data, add new functionality, and automate everyday processes. API integration is approached with attention to security, especially for products that handle sensitive information or operate in regulated industries.

Beyond building new APIs, they integrate existing services, modernize legacy systems, and improve API performance through testing, maintenance, and optimization. Their experience covers integrations with payment platforms, cloud providers, authentication services, communication tools, CRM systems, and other business applications. The company also supports projects that require API audits, documentation, and long-term maintenance as products continue to evolve.

21CENTURY.TECH develops web applications, MVPs, and custom software using a workflow that combines senior software engineers with AI-assisted development tools. They focus on reducing development time while keeping engineering decisions, architecture, testing, and code reviews under human supervision. Third-party API integration is part of their development process for projects that require external services, payment systems, or cloud platforms.

Their team works with both new products and existing applications. Besides building software from scratch, they also refactor legacy code, implement CI/CD pipelines, and improve existing systems. Daily project updates and continuous code reviews are part of their delivery process, helping clients track development throughout each stage of the project.

Seed Technologies develops software solutions that include third-party API integration for businesses looking to connect existing applications with external systems. Their work covers both integrating available APIs and building custom web APIs that allow other platforms to exchange data with internal business software. This approach helps organizations automate routine operations and reduce manual data handling across different systems.

Along with API integration, they support projects involving legacy software modernization, making older applications available through web technologies without replacing the entire system. Their development process also includes API planning, implementation, and hosting, giving businesses a single environment for managing connected applications and services.

Invoidea Technologies builds custom APIs and connects businesses with third-party platforms that support everyday operations. Their API integration work covers payment services, business applications, cloud platforms, and other external systems that need to exchange information reliably. Security, documentation, and long-term compatibility are included throughout the integration process, helping connected systems remain easier to manage.

Different industries often require different integration approaches, so their projects range from eCommerce and healthcare to logistics, finance, and education. Alongside third-party API integration, they develop custom APIs, monitor API performance, and configure gateways that help regulate traffic, authentication, and communication between connected applications.

Itexus develops software for financial organizations and businesses that require secure integrations between multiple systems. They work on banking platforms, payment solutions, investment products, lending software, and other fintech applications where third-party API integration is an essential part of the system architecture. Their projects commonly involve payment gateways, banking APIs, KYC providers, trading platforms, and financial data services.

Their engineering team also works on product discovery, legacy modernization, cloud infrastructure, DevOps, quality assurance, and software maintenance. In addition to API integration, they support businesses with compliance-focused development, cybersecurity, AI implementation, and long-term technical support for enterprise applications operating in regulated environments.

TechAhead develops APIs that connect websites, mobile apps, enterprise software, and external platforms into a single working environment. Their integration projects include payment providers, CRM systems, shipping services, cloud platforms, and other third-party applications that support day-to-day business operations. The focus is on creating stable connections that allow information to move securely between systems.

Every integration project starts with planning the API architecture before development begins. From there, the team handles implementation, testing, deployment, and ongoing monitoring to keep connected services running smoothly. They also work with legacy systems, helping businesses connect existing software with modern applications without rebuilding everything from scratch.

EvinceDev offers third-party API integration as part of custom software and application development projects. Their team connects web and mobile applications with external services, allowing businesses to extend functionality without building every feature from the ground up. Depending on the project, integrations may include mapping services, analytics platforms, cloud storage, social media, travel services, or eCommerce tools.

Each integration follows a structured development process that covers research, design, testing, deployment, and ongoing maintenance. Since the company works across industries such as healthcare, logistics, retail, fintech, education, and travel, API integrations are adapted to the specific workflows and data requirements of each project.

A-listware provides software development, IT consulting, and team augmentation services for companies that need additional engineering resources or complete product development. They work with businesses of different sizes, including startups, small and mid-sized companies, and enterprises. Their projects often involve third-party API integrations that connect business applications, cloud services, ERP systems, CRM platforms, and other software into a single workflow.

Their work covers the full software development lifecycle, from planning and development to testing, infrastructure management, and long-term support. They also help companies modernize legacy systems, build cloud applications, strengthen cybersecurity, and manage development teams that operate as an extension of an in-house engineering department. Their experience across multiple industries allows them to handle integration projects that require both technical knowledge and ongoing maintenance.

COAX specializes in connecting business systems through third-party API integration, helping organizations bring together software that would otherwise operate separately. Their projects often involve CRM, ERP, document management platforms, communication tools, payment gateways, logistics software, and cloud services. By linking these systems, they help businesses reduce repetitive manual work and keep information synchronized across departments.

Their experience also covers modernizing legacy software, extending existing applications with external APIs, and selecting integration solutions that fit technical and business requirements. Every project moves through research, architecture, development, testing, and maintenance, giving connected systems room to evolve as business processes change.

UX 4Sight approaches software development from the perspective of usability, combining application design with custom development that supports integration with external systems when needed. Their projects include web, mobile, cloud, and enterprise applications where third-party APIs can extend functionality, connect business tools, and support smoother user experiences across different platforms.

The company follows a structured process that includes planning, design, development, testing, deployment, and post-launch support. Alongside application development, they focus on building interfaces that work well with integrated services, making connected systems easier for end users to navigate while supporting long-term product maintenance.

Moon Technolabs develops API solutions that help businesses connect their applications with third-party platforms and internal systems. Their API integration services cover payment gateways, mapping services, social networks, cloud applications, and other external tools that support day-to-day business operations. Along with third-party integrations, they build custom APIs that improve data exchange and make it easier to add new features as products grow.

Each integration follows a structured process that includes planning, API design, development, testing, deployment, and ongoing maintenance. Security, scalability, and performance are considered throughout the project, while support continues after launch to keep integrations working as external services and business requirements change.

Opal Infotech focuses on maintaining and managing third-party integrations that keep business websites connected with external services. Their approach centers on API updates, plugin compatibility, and continuous monitoring to help websites stay stable as connected platforms evolve. The team works with payment gateways, CRM systems, analytics tools, and other third-party services that play an important role in everyday website operations.

Keeping integrations reliable requires more than connecting an API once. They monitor API version changes, test updates before deployment, resolve compatibility issues, and maintain performance across platforms such as WordPress, Shopify, and Laravel. Their maintenance process is built around preventing disruptions caused by changing third-party services and outdated integrations.

CodeVix builds custom web applications that include third-party API integrations as part of the overall software architecture. Their projects connect websites and business platforms with external services through REST APIs, GraphQL APIs, and middleware solutions. API integrations are used across business websites, eCommerce platforms, client portals, dashboards, and custom web applications, making it easier for different systems to exchange information.

Development moves through discovery, design, implementation, testing, launch, and long-term support. As projects grow, additional integrations can be added without rebuilding the core application, allowing businesses to expand functionality while keeping connected services organized and easier to maintain.

Flatworld Solutions develops API integrations for enterprise environments where multiple business platforms need to exchange information in real time. Their projects connect CRM, ERP, cloud applications, and internal systems through APIs built on standards such as REST, GraphQL, and gRPC. The focus is on creating reliable communication between applications while supporting growing business infrastructure.

Security, scalability, and performance are included throughout the integration process. The company also works with microservices and containerized environments, helping businesses connect modern applications with existing systems while supporting ongoing API management as software ecosystems continue to expand.

Sage IT focuses on API integration for enterprise environments where different business systems need to exchange information without interrupting daily operations. Their services cover third-party API integration, custom API development, cloud APIs, and API management for platforms such as CRM, ERP, HRMS, databases, cloud storage, and SaaS applications. The goal is to help organizations keep data flowing between systems that support different parts of the business.

Beyond implementation, the company handles API strategy, testing, managed services, and long-term support. Their integration projects often involve connecting cloud platforms, financial systems, e-commerce tools, and enterprise software, allowing businesses to maintain consistent data across applications while making future integrations easier to manage.

Velvetech builds API solutions that connect business applications, cloud services, and third-party platforms into a single environment where information can move without manual intervention. Their projects include both custom API development and integrations with existing services, giving businesses a practical way to expand software functionality while keeping systems connected.

The integration process is planned alongside the overall software architecture, making APIs part of a larger application ecosystem instead of treating them as separate components. Development, implementation, maintenance, and future updates are handled within the same workflow, which helps connected applications remain compatible as business requirements change.

SECL Group specializes in third-party API integration for software products that depend on continuous data exchange between multiple systems. Their projects cover integrations with payment gateways, social media platforms, e-commerce services, mapping tools, and custom business applications. Depending on project requirements, they also connect legacy software with modern APIs and develop custom integrations when existing solutions do not fit the workflow.

Every integration goes through planning, API selection, development, documentation, testing, and ongoing maintenance. The company places emphasis on stable communication between connected systems, detailed documentation, and long-term support, making API integration part of a broader software development process instead of a one-time implementation.