Many software testers get by with a minimal toolset: a few browsers, built-in developer tools, a SQL client, and maybe an HTTP inspector. Testing APIs demands more. The API testing tool landscape is crowded, and while most tools overlap significantly in core capability, each has a distinct area where it excels. This guide outlines the most commonly used options so you can match the right tool to your team’s specific needs.
Note: This article is based on a summary originally attributed to programmableweb.com. Pricing figures and product details reflect the original publication date of December 2017 and may have changed significantly. Always verify current pricing and feature sets on the vendor’s official website before making a purchase decision.
SmartBear ReadyAPI
ReadyAPI (formerly Ready API) is a commercial suite from SmartBear that bundles several specialized testing tools into one platform:
- SoapUI Pro – Despite the name, this tool handles REST, SOAP, and web service APIs. It supports recording and replaying requests, building full test suites, importing Swagger or RAML description files to accelerate test creation, and running tests via command-line for CI integration.
- LoadUI Pro – A dedicated load and performance testing tool. It lets testers vary data volumes and simulated user counts to assess API scalability.
- Secure – A security testing tool specifically designed for API endpoints.
- ServiceV – Supports creation, deployment, and management of virtual API environments, useful when a dependent service is unavailable during testing.
- AlertSite – An API monitoring component that tracks usage and behavior across development, test, and production environments.
ReadyAPI is a strong choice for teams that need an integrated platform covering functional, performance, security, and monitoring testing under one license. A free, non-commercial version of SoapUI (without the “Pro” features) is available as an open-source download.
Postman
Postman began as a free Chrome browser extension and evolved into one of the most widely used standalone API testing tools available. Its core functionality allows testers to store, organize, and execute API calls. Calls can be chained together so that each request is predicated on the response from the previous one, which is essential for testing stateful workflows.
Key capabilities in paid tiers include:
- Shared team collections for collaborative testing
- API monitoring
- Environment variable management across multiple workspaces
- Dedicated product support
Postman is particularly well suited for teams that want a GUI-driven workflow with a low barrier to entry. Its free tier is generous enough for individuals and small teams, and the paid tiers scale to enterprise needs. Note that pricing and plan names have changed considerably since 2017—check postman.com/pricing for current details.
Airborne (Ruby Library)
Airborne is a free, open-source Ruby library for testing REST APIs. Unlike GUI-driven tools, Airborne is a code-first solution: tests are written in Ruby using the RSpec convention, giving developers full programmatic control over test logic.
Common assertion helpers include:
expect_json– Assert specific JSON values in the response bodyexpect_json_types– Assert the data types of JSON fieldsexpect_status– Assert the HTTP status code of the response
Because tests are plain Ruby code, integrating Airborne with a CI/CD pipeline is straightforward—any system that can run a Ruby process can execute Airborne tests. The library is installed via RubyGems. Teams already working in Ruby will find the learning curve minimal; those unfamiliar with Ruby may prefer a GUI-based alternative.
Command-Line Tools: curl and HTTPie
Both curl and HTTPie are free, open-source command-line utilities for making HTTP requests. They are not designed for building large automated test suites, but they are invaluable for:
- Rapidly exploring an unfamiliar API during development
- Issuing one-off requests to isolate a suspected bug
- Scripting simple smoke tests in a shell pipeline
Both tools support basic authentication and token-based auth. HTTPie is often preferred for its more human-readable output and intuitive syntax, while curl is nearly universally available and extremely well documented. For quick exploratory work or lightweight CI checks, either tool is a practical starting point that requires no additional installation in most Unix environments.
API Science
API Science is a commercial monitoring and testing tool aimed at APIs running in production. Its strengths are operational visibility rather than pre-release functional testing:
- Quick setup and low configuration overhead
- Monitoring of third-party and internal APIs
- Alerting when an API degrades or fails
- A unified dashboard showing health and usage metrics
API Science is best suited for teams that need continuous visibility into production API behavior rather than teams focused purely on pre-release testing. Pricing as of the original article started at $29 per month with a free 30-day trial; verify current plans directly with the vendor.
API Metrics
API Metrics is another production-focused tool, but with an emphasis on performance rather than general monitoring. Instead of virtualized calls, it executes real authenticated requests with actual data against a live API and collects the resulting performance data. This gives development teams accurate, real-world latency and throughput measurements rather than synthetic estimates.
API Metrics offers self-serve, supported, and managed service tiers. Contact the vendor for current pricing. This tool is most relevant for teams managing SLA obligations or troubleshooting production performance regressions.
How to Choose the Right Tool
Before selecting a tool, define the problem you are trying to solve. The following questions can help narrow the field:
- What kind of testing do you need? Functional correctness, load/performance, security, or production monitoring each calls for different tooling.
- Where does testing happen? Pre-release testing in a CI pipeline has different requirements than continuous monitoring in production.
- What is your team’s technical profile? Developers comfortable with Ruby or scripting languages may prefer code-first tools like Airborne or curl. Teams with mixed skill sets may benefit from the GUI of Postman or ReadyAPI.
- What are your collaboration and reporting needs? If multiple team members must share test collections or review results, look for tools with team features and dashboards.
- What is your budget? Open-source options (Airborne, curl, HTTPie, SoapUI community edition) cover many use cases at no cost. Commercial suites add polish, support, and integrated monitoring.
No single tool covers every scenario perfectly. Many teams use a combination: curl or HTTPie for quick exploration, Postman or Airborne for functional test suites, and a dedicated monitoring tool like API Science or AlertSite for production observability.
Summary Comparison
| Tool | Type | Cost | Best For |
|---|---|---|---|
| SmartBear ReadyAPI | Commercial suite | Paid (SoapUI free tier available) | Integrated functional, load, security, and monitoring |
| Postman | GUI client | Free + paid tiers | Team collaboration, chained requests, monitoring |
| Airborne | Ruby library | Free / open source | Code-first testing, CI integration, Ruby teams |
| curl / HTTPie | CLI utilities | Free / open source | Exploratory testing, scripting, quick debugging |
| API Science | SaaS monitor | Paid (free trial) | Production monitoring, third-party API health |
| API Metrics | SaaS monitor | Paid | Production performance measurement |
The API testing landscape continues to evolve rapidly. Evaluate tools against your team’s current workflow, and revisit your toolset periodically as your APIs and organizational needs grow.