Postman - The Collaboration Platform for API Development
Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
Insomnia REST - The most intuitive cross-platform REST API Client ð´
AppDynamics - Get real-time insight from your apps using Application Performance Management—how they’re being used, how they’re performing, where they need help.
Postwoman - An online, open source API request builder
Zabbix - Track, record, alert and visualize performance and availability of IT resources