Best API Development & Testing Tools in 2026

Generate lifelike AI voices in 29 languages, clone voices, and enable real-time speech

4.6 /5 across G2 and Capterra · 1,236 ratings, Sep 2026

ElevenLabs provides the most realistic AI voice technology for content creators and developers. Generate lifelike speech from text in 29 languages. Clone voices with just minutes of audio samples. Real-time voice synthesis for conversational AI applications. API for developers building voice-enabled products. AI voices indistinguishable from human speech.

Send and sign documents with ease, integrated with Dropbox

4.7 /5 on G2 · 2,283 ratings, Sep 2026

Dropbox Sign is an electronic signature platform integrated with Dropbox. Send documents for signature with a simple, intuitive experience. Templates streamline recurring signature workflows. API enables embedding signatures in your applications. Legally binding and compliant with major regulations. E-signatures that feel native to the Dropbox experience.

Payment infrastructure for the internet

4.4 /5 across G2 and Capterra · 3,839 ratings, Sep 2026

Stripe is a financial infrastructure platform for internet businesses. Accept payments from anyone, anywhere. Billing handles subscriptions and invoicing. Connect powers marketplace payments. Treasury provides banking as a service. The payments infrastructure that powers millions of businesses from startups to Fortune 500 companies.

Unify apps, data, and devices across cloud and on-premise

4.4 /5 across SourceForge, G2 and Capterra · 1,468 ratings, Sep 2026

MuleSoft Anypoint Platform is an enterprise integration and API management platform owned by Salesforce. It connects applications, data sources, and devices across on-premise and cloud environments through a unified architecture. The platform includes API design, development, and governance tools alongside pre-built connectors for hundreds of systems including Salesforce, SAP, Workday, and AWS. MuleSoft Composer provides low-code integration for business teams, while Robotic Process Automation (RPA) handles legacy system workflows. Intelligent Document Processing (IDP) extracts data from unstructured documents using AI. The platform also supports AI agent development through MuleSoft for Agentforce. Used by enterprises for digital transformation, it is the market leader in integration platforms, though its pricing starts at $57,000/year, making it suitable for mid-market to enterprise organizations.

API platform for building and using APIs

4.6 /5 across G2 and Capterra · 2,311 ratings, Sep 2026

Postman is an API development platform used by over 30 million developers and 500,000 organizations worldwide. It provides a unified workspace for designing, testing, documenting, and monitoring APIs across HTTP, GraphQL, gRPC, WebSocket, and MQTT protocols. Teams can collaborate through shared workspaces, collections, and mock servers while maintaining version control via native Git integration. The platform includes an AI-powered agent mode for automating repetitive API tasks, an API catalog for internal service discovery, and a CLI for CI/CD pipeline integration. Postman supports the full API lifecycle from spec design through production monitoring, making it the industry standard for API-first development workflows.

Reliable event infrastructure for webhooks and external event streams.

4.5 /5 across G2 and Capterra · 2,271 ratings, Oct 2026

This platform provides robust event infrastructure designed to manage the full lifecycle of external events, from ingestion to delivery and observability. It ensures that every event, whether from third-party webhooks or outbound event streams, is received, processed, and monitored reliably at scale, offering complete visibility and control. It's built for engineering teams dealing with event-driven systems, offering features like built-in event queueing to handle traffic spikes and destination failures, automatic issue management with event replay capabilities, and flexible routing and transformation of events. The platform integrates seamlessly with any tech stack, supporting various backends and allowing declarative infrastructure definition through API or Terraform. The core value proposition is to eliminate the headaches associated with managing webhooks and external events, such as missed events, retries, and debugging. By providing a scalable, secure, and compliant solution, it allows developers to focus on building their applications rather than on the complexities of event infrastructure, ensuring peace of mind even with high volumes of event data.

Build communication features with programmable APIs for SMS, voice, video, and more

4.2 /5 across G2 and Capterra · 2,426 ratings, Sep 2026

Twilio is a cloud communications platform providing APIs for SMS, voice, video, WhatsApp, email, and authentication services. It enables developers to programmatically send messages and make calls.

Integration platform as a service

4.7 /5 on G2 · 1,025 ratings, Mar 2026

Celigo is an enterprise integration platform as a service (iPaaS) that connects applications, automates workflows, and unifies data across business systems. It provides pre-built connectors, API management, EDI/B2B capabilities, and AI-powered error resolution, all on a flat-rate pricing model with no per-transaction fees. Named a Gartner Peer Insights Customers' Choice for iPaaS, Celigo serves teams across IT, finance, e-commerce, and operations who need to eliminate manual data transfers between systems.

Connect 1000+ apps with AI-powered no-code automations

4.7 /5 across G2 and Capterra · 916 ratings, Sep 2026

Albato is an AI-driven integration platform that connects 1,000+ applications through a no-code visual builder. It supports two-way data synchronization, webhook triggers, scheduled automations, and bulk data migration between business tools. With built-in AI capabilities for advanced models, teams can add intelligent data transformation directly into workflows. Albato positions itself as a cost-effective Zapier alternative at roughly lower pricing, serving 200,000+ users from small businesses to enterprises with a white-label embedded integration option.

Multi-carrier e-commerce shipping API with discounted rates

4.6 /5 across G2 and Capterra · 903 ratings, Sep 2026

Shippo provides shipping API and discounts. Multi-carrier shipping for e-commerce-labels and tracking with rate shopping. The carrier options are many. The rates are discounted. The API is straightforward. E-commerce shipping through APIs often uses Shippo for multi-carrier access.