flowscope
Copyright (c) 2026 flowscope contributors
This product is licensed under MIT OR Apache-2.0 (see LICENSE-MIT and
LICENSE-APACHE), WITH ONE EXCEPTION described below.
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JA4S — FoxIO License 1.1 (opt-in `ja4plus` feature)
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The JA4S server-side TLS fingerprint implementation in
`src/tls/ja4s.rs` is part of the JA4+ suite and is licensed under the
**FoxIO License 1.1** (see LICENSE-FoxIO-1.1), NOT under flowscope's
MIT/Apache-2.0 terms. JA4+ methods are **patent pending**. "JA4+" is a
trademark of FoxIO, LLC.
This code is compiled **only** when the off-by-default `ja4plus` cargo
feature is enabled. It is, however, present in the published source
distribution regardless of features — so per the FoxIO License 1.1, this
notice and the license text travel with every copy.
The FoxIO License 1.1 permits **non-commercial** use, modification, and
distribution (personal, academic, internal evaluation, and internal
business use where JA4S is not monetized). **Commercial use** — selling
JA4+ fingerprinting as part of a product or service, or otherwise
monetizing it directly or indirectly — requires a separate **OEM license
from FoxIO, LLC**. See https://github.com/FoxIO-LLC/ja4 and
https://github.com/FoxIO-LLC/ja4/blob/main/License%20FAQ.md
The default flowscope build, and the `tls-fingerprints` feature
(JA3 + JA4 TLS *client* fingerprints), are **BSD-3-Clause-equivalent /
royalty-free** — JA3 (Salesforce) and JA4 client are open-source. Only
`ja4plus` (JA4S) carries the FoxIO terms.