🔒
Fully local & private
No account, no cloud sync, no telemetry. Your data never leaves your machine.
Synapse
Synapse
Synapse is an offline, privacy-first desktop API client for REST and GraphQL — a free alternative to Postman, Bruno, and Insomnia that keeps your data 100% on your machine.
No login. No cloud. No telemetry. Just your APIs, your files, your control.
"id": "login",
"name": "Login",
"method": "POST",
"url": "{{selector.environment.BASE_URL}}/auth/login",
"headers": {
"Authorization": "Bearer {{secrets.API_KEY}}"
},
"scriptLines": [
"TOKEN = response.body.accessToken",
"run:parse-token"
]Everything is stored as plain files on your filesystem. It works offline. It works with Git. It works the way developers expect tools to work.
No account, no cloud sync, no telemetry. Your data never leaves your machine.
Fast, lightweight app for Linux, macOS, and Windows. No bloated web engine.
Plain JSON files you can diff, branch, merge, and review in PRs like any other code.
One selector swaps environment, region, version, or credential profile across all requests via {{templates}}.
Edit a JSON file on disk and the UI updates instantly. No manual reload.
No cloud paywall, no per-seat pricing, no feature tiers.
Import a .env once; Synapse encrypts it with a machine-local key, stored outside your repo. Use as {{secrets.KEY}} — nothing tracked in Git or readable by AI agents.
Structured JSON workspace in predictable paths, easy for LLMs and AI agents to read, generate, and edit.
Synapse is a local-first API client for developers and QA engineers.
Without the account requirement, cloud sync, or subscription.
With a native desktop GUI and live environment switching.
Without telemetry or forced cloud features.
A space is just a folder. Collections, selectors, and scripts are plain files you control.
Each space is a plain folder with a workspace.json, a collections/ folder of requests, and a selectors/ folder — optionally scripts/.
my-space/
├── workspace.json ← space name
├── collections/ ← HTTP requests
├── selectors/ ← dropdowns
└── scripts/ ← automationEach .json in collections/ is one request. Templates work in url, headers, queryParams, and body.
{
"method": "GET",
"url": "{{selector.env.BASE_URL}}/products/{{selector.product}}"
}Selectors are dropdown chips in the toolbar. Flip one and every request that references it retargets instantly — environments, regions, identities.
{{selector.environment.BASE_URL}}
{{selector.credentials.USERNAME}}
{{selector.product}}Extract values from responses into session variables, or run custom Kotlin .kts scripts for JWT decoding, HMAC signatures, and multi-step flows.
TOKEN = response.body.accessToken
run:parse-token
# → {{script.TOKEN}} everywhereAPI keys, tokens, and passwords don't belong in plain JSON or Git history. Import a .env once and Synapse keeps them in an encrypted, machine-local vault that lives outside your repository.
{
"headers": {
"Authorization": "Bearer {{secrets.API_KEY}}"
}
}At send time Synapse decrypts the value on the fly and injects it.
Everything you might want to know before you download.
Yes. Synapse is a local-first API client with no subscription. Unlike Postman, it requires no account, runs entirely offline, and stores your collections as plain files on your own machine — nothing is synced to a cloud.
Like Bruno, Synapse is local-first and Git-friendly. The difference is that Synapse stores everything as plain JSON (not a custom DSL), is built to stay local and offline, and is explicitly optimized to be AI/LLM-friendly so agents can generate and edit your collections directly.
Yes. Synapse covers the same REST and GraphQL workflows without telemetry, accounts, or forced cloud features. Your collections stay as plain JSON files on disk that you can version in Git — no proprietary database or sync service.
Completely. There is no sign-in, no cloud, and no telemetry. The only network traffic Synapse makes is the HTTP requests you send to your own APIs.
Yes. Send a POST request with a JSON body containing your GraphQL query and variables.
In a directory you choose on your filesystem. Each "space" is a folder containing workspace.json, a collections/ folder of requests, and a selectors/ folder — all plain JSON you can commit to Git.
macOS, Windows, and Linux. Synapse is a native desktop app built with Compose Multiplatform.
Yes — that's a core design goal. Because every request and selector is structured JSON in a predictable path, LLMs and coding agents can scaffold entire workspaces, add endpoints, or refactor variables with no special tooling.
Free, native, and offline. Pick your platform and start sending requests in seconds.
.dmg installer · Apple Silicon & Intel
Download.msi installer · 64-bit
Download
.deb package · Debian / Ubuntu
DownloadFree, native, and offline — no account required.
Do you like the app? We'd be happy about your support!
Synapse is built with love by a small team — no VC funding, no subscriptions, no ads. If Synapse saves you time or makes your workflow better, consider buying us a coffee. Every contribution helps us keep the app free and actively maintained.
☕ Buy us a coffeeThank you for being part of the Synapse community! 💜