Postman keeps every response you have ever received
Response history, collections and installed runtimes accumulate in an app that feels stateless. Where the data is and what is safe to clear.
An API client feels stateless: you send a request, you read the response, you move on. Underneath, most of them keep every response body, every console log and every version of every collection, and the ones that sync also keep a local mirror.
Where to look
du -sh ~/Library/Application\ Support/Postman \
~/Library/Application\ Support/Insomnia \
~/Library/Caches/Postman 2>/dev/null | sort -hThe large items are the response history database and, in Electron based clients, the usual Cache and Code Cache folders. Response history is the one that surprises people: downloading a large file through the client stores that response.
Clearing history without losing collections
Both major clients separate collections, which are your work, from history, which is a record. Clear the history from inside the app, where it is a single action, rather than removing the data folder, which takes your collections and environments with it.
- Collections and environments. Keep. Export them if you are about to do anything drastic.
- Response history. Safe to clear, and usually the bulk.
- Console logs. Safe.
- Cache folders. Safe, rebuilt on next launch.
The export first rule
# Postman: File, Export, for each collection and environment
# Insomnia: Application, Preferences, Data, ExportCollections that exist only locally are as valuable as source code and are stored in a database rather than as files you would notice. Exporting them takes a minute and turns a risky cleanup into a safe one.
Where this sits
API clients are rarely the largest thing on a developer Mac. They belong to the same category as editor caches and IDE indexes: individually modest, collectively worth a look, and all of them rebuildable except the part that is your own work.
Common questions
Where does Postman store data on a Mac?
In ~/Library/Application Support/Postman, with cache folders under ~/Library/Caches. The response history database is usually the largest part, along with the standard Electron cache folders.
Is it safe to clear Postman's history?
Yes. History is a record of past requests and responses, not your work. Collections and environments are stored separately and are unaffected by clearing history from inside the app.
Why is my API client using gigabytes?
Response bodies. Every response is kept, including large downloads made through the client, so a few file transfers can dominate the folder.
How do I back up Postman collections before cleaning up?
Export each collection and environment from the File menu. They live in an app database rather than as visible files, so exporting is the only way to keep them if the data folder is removed.