API Testing

A full-featured API client with pre/post-request scripts, declarative assertions, a collection runner, GraphQL / WebSocket / gRPC support, and one-click Postman import.

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What You Get

Postman import

Drop a Postman v2.1 export — collections, environments, scripts, auth configs. One click migration.

Multi-protocol

REST, GraphQL (with schema introspection), WebSocket, SSE, gRPC. One UI for all four.

Pre/post scripts

JavaScript sandbox via Node's vm module. Set variables, transform requests, parse responses.

Declarative assertions

Status, header, JSONPath, response time — point-and-click, no scripting required.

Collection runner

Run an entire collection sequentially or in parallel. Per-request and aggregate results.

Code generation

Generate cURL, fetch, axios, Python requests, or Go code from any request, ready to paste.

Frequently Asked Questions

Can I import my Postman collections?

Yes — drop the JSON export onto the import dialog. Collections, environments, scripts, and auth all come over.

Does it work offline?

The current build is web-based. Electron desktop builds are in the roadmap.

How is this different from Thunder Client?

Thunder Client is a VS Code extension. Arythmatic Flow is a full standalone app with monitoring, workflows, and team collaboration in addition to the API client.

Does it support GraphQL schema introspection?

Yes — paste a GraphQL endpoint, hit introspect, browse the schema in the sidebar.