The first workflow is bulk request bodies. Many APIs accept a JSON array in a single request to create or update multiple resources in one call. The Stripe API, Shopify Admin API, HubSpot batch endpoints, and most modern REST services support this pattern. The data often originates as a CSV from a product or marketing team. Convert the CSV to a JSON array in FixTools, paste into Postman as the raw request body with Content-Type application/json, and the API processes all records in one round trip. The conversion takes seconds and the JSON is ready to send.
The second workflow is the Postman Collection Runner. The runner accepts a JSON data file where each element drives one iteration of the collection, with the element fields available as variables in the requests. CSV data converts to exactly this shape: a JSON array of objects. Save the converted JSON as a .json file, attach it as the data file in the runner, and each row drives one iteration. The runner supports CSV data files directly too, but the JSON format is more flexible because it supports nested values for richer test scenarios.
Type inference matters more in Postman than in some other tools. Postman variable substitution and JSON request bodies are sensitive to whether a value is a number, boolean, or string in the source data. A field that should be a numeric quantity but lands as a string can cause the API to reject the request or store the wrong type. FixTools produces typed JSON automatically, so quantity columns come out as numbers, active flag columns come out as booleans, and the request body matches the API schema without manual type fixing.
Privacy matters for test data too. Even synthetic test data often resembles real customer records closely enough that uploading it to a third-party converter feels uncomfortable. FixTools converts in the browser with no upload, so even production-realistic test fixtures stay on your machine. The clipboard copy goes directly to Postman without any intermediate cloud service touching the data.