Syncthing

TAS Score: S3/3 — D5/5 — A3 / T2

Assessment criteria: v1.1. Context: self-hosted · single-user · Docker. Last verified: 2025-05.

Brief Description

Peer-to-peer file synchronisation tool that keeps folders in sync across multiple devices — without a central server, without cloud accounts, without trusting a third party.

Architectural Role

Storage layer: provides continuous, encrypted file sync between devices over the local network or via relay. Replaces Dropbox, Google Drive, and similar cloud sync services.

Formal Assessment

S1: Pause

Test	Result	Evidence
Can you stop the process without a special shutdown procedure?	✅ Yes	`docker stop syncthing` or close the app. Clean shutdown.
After stopping, is all data still on disk in a readable state?	✅ Yes	Files are ordinary files on your filesystem. Nothing changes when Syncthing stops.
Can you restart and continue where you left off?	✅ Yes	Restart → resumes sync from where it left off. No re-registration.

S1 = Yes

S2: Exit

Test	Result	Evidence
Is there a documented export mechanism?	✅ Yes	No export needed. Files ARE your data — they live on your filesystem as regular files.
Does the export include ALL user data?	✅ Yes	All data is always on disk. Syncthing adds only a `.stfolder` marker and `.stversions` for versioning.
Is the export in a standard, reusable format?	✅ Yes	Files are in their original format. Stop Syncthing → files remain exactly as they are.
Can another tool import the exported data?	✅ Yes	Any tool can read the files. No import step needed.

S2 = Yes

S3: Recoverability

Test	Result	Evidence
Does the service support backups?	✅ Yes	Files are regular files — any backup tool works. Built-in file versioning (`.stversions`).
Can you restore from backup to a working state?	✅ Yes	Copy files back. Reinstall Syncthing. Add folder. Done.
Does a restore give you back the SAME state?	✅ Yes	All data restored. Device IDs regenerated (expected), but no data loss.

S3 = Yes

Autonomy Level

S1	S2	S3	Level
Yes	Yes	Yes	A3

Transparency Level

Test	Result	Evidence
Source code publicly available?	✅ Yes	github.com/syncthing/syncthing
License OSI-approved?	✅ Yes	MPL-2.0

T = T2

Diagnostic Score

#	Question	Result	Evidence
D1	Personalisation	✅ Clean	No analytics. No user tracking. No recommendation engine. Usage reporting is opt-in and anonymous.
D2	Urgency	✅ Clean	No notifications beyond sync status. No forced updates. No deadlines.
D3	Hidden cost	✅ Clean	No ads. No data sharing. No identity requirements. No lock-in.
D4	Transparency fragility	✅ Clean	Value comes from file sync, not from information asymmetry. Fully transparent operation.
D5	Trajectory	✅ Clean	MPL-2.0 since launch (2014). Syncthing Foundation governs the project. No paid tier. No corporate owner. Discovery/relay servers are self-hostable.

D-score: D5/5 (0 concerns)

Counterarguments

Claim	Challenge	Resolution
A3: fully autonomous	Relies on discovery servers to find peers over the internet	Discovery servers are operated by the Foundation but fully self-hostable. LAN sync works without them entirely.
A3: fully autonomous	Relay servers needed when direct connection fails (NAT)	Relay servers are optional, self-hostable, and only carry encrypted data. LAN sync never uses them.
D5: no concerns	Usage reporting exists	Opt-in, anonymous, aggregated. Disabled by default in Docker deployments. Not a concern.

Configuration (Minimal)

services:
  syncthing:
    image: syncthing/syncthing:latest
    container_name: syncthing
    ports:
      - "8384:8384"
      - "22000:22000"
    volumes:
      - ./syncthing-config:/var/syncthing/config
      - ./syncthing-data:/var/syncthing/data
    restart: unless-stopped

Alternatives

Alternative	Autonomy	Notes
Nextcloud	A3 / T2	Heavier, server-centric, but offers calendar/contacts/office.
Resilio Sync	A2 / T0	Similar P2P model but proprietary and closed source.

Trajectory

Direction: stable.

Syncthing is MPL-2.0 licensed and community-governed by the Syncthing Foundation. Development has been active and consistent since 2014. No corporate ownership, no paid tier, no cloud lock-in.

Signal	Status	Evidence
License	✅	MPL-2.0; no changes since launch.
Feature gating	✅	No paid tier; all features free.
Self-hosting	✅	Discovery and relay servers are self-hostable.
Governance	✅	Syncthing Foundation; community-driven.

Signal key: ✅ opening · ➖ neutral · ⚠️ closing

Sources

Website: https://syncthing.net
Documentation: https://docs.syncthing.net
Repository: https://github.com/syncthing/syncthing
Docker image: https://hub.docker.com/r/syncthing/syncthing
Community: https://forum.syncthing.net