Any language that can spawn a process. FYLO ships as a single binary that speaks a JSON machine protocol over stdin/stdout; drop-in shims are provided for Python, Ruby, Node/TypeScript, PHP, Go, Rust, C#, Java, and Dart, and the protocol is tested in CI against even more. For platforms that can't spawn the binary there are local-only clients that embed the engine on-device — the browser bundle, native iOS (Swift) and Android (Kotlin) clients, and a Flutter client.

Yes — Fylo Explorer is a browser UI over a real FYLO root on your disk, opened through the File System Access API. Pick the folder once and browse collections, inspect documents, and filter with SQL WHERE expressions (role = 'admin' AND age >= 30). It is read-only by default — the engine rebuilds indexes into a copy-on-write overlay, never touching the folder — with opt-in writes that go through the engine. Document queries run in a worker with Wasm acceleration and automatic JavaScript fallback. Chromium-only, since Firefox and Safari do not implement real-folder access.

FYLO owns local storage and querying — the index is always local, never in the query path. For a hands-off backup, point sync.s3 at a dedicated bucket prefix and FYLO mirrors the whole root (documents, buckets, index, catalog, vcs) to S3: touched files are mirrored on write and reconcile() makes that prefix match the root exactly. Prefer your own client? onWrite / onDelete sync hooks still notify it in await-sync or fire-and-forget mode.

Writes are serialized per collection with advisory file locks. There are no cross-collection atomic commits — declare related objects as their own collections and join them at query time with joinDocs.

Fields listed in a schema’s $encrypted array are stored with AES-GCM. Equality lookups use HMAC blind indexes, so queries work without decrypting — with the documented trade-off that value repetition counts are observable.

Yes. Write it with .as({ gid: editorsGid, mode: 0o660 }), then authenticated group members read, update, or delete with .as({ uid: memberUid }). FYLO resolves membership from the host POSIX group database or your trusted groupsForUid resolver; callers cannot claim their own groups. Group write permission is required — 0o600 remains owner-only.