This repository contains IETF-style Internet-Draft specifications for the Fossil source code management system. Fossil is unusual among SCMs in having substantial written specifications and source documentation. These drafts take that specification to a new level of formality, but the source documents and code are sufficiently detailed and consistent that the task is mostly transcribing formats rather than reverse-engineering intent. This project will hopefully help fulfil the goal from 2005 of Fossil being at least a 100-year format.
The first scope for these Internet drafts is to correctly and sufficiently document how Fossil works in 2026, particularly the wire sync protocol version 3, the artifacts and the algorithms for making it all work. This will ensure that all conformant implementations will work with each other and with the canonical Fossil. There has been a long-standing desire in the Fossil community to improve protocol version 3, and to introduce other artifacts such as the S-Card, both of which are examples of subsequent revisions to these Internet drafts.
Like any RFC series, these drafts are intended to promote multiple, independent implementations which can share Fossil repositories with each other. You will find here:
| Draft | Status |
|---|---|
draft-fossil-artifact-format-00.txt |
Tested draft; multiple implementations |
draft-fossil-delta-format-00.txt |
Tested draft; multiple implementations |
draft-fossil-sync-protocol-00.txt |
Tested draft; multiple implementations |
draft-fossil-repo-state-00.txt |
Tested draft; multiple implementations |
draft-fossil-submanifests-00.txt |
Untested notes; no implementations |
Use of LLMs
These particular drafts are about text transformation, which is one of the main use cases of LLMs. After the initial hand-rolled efforts, we moved to a single LLM prompt and then later developed a workflow for refining the drafts by iterating between Fossil documentation, Fossil source code, RFC test harnesses, and the alternative implementations. We ship some LLM source material:
- the workflow prompts and supporting docs directing LLM agents to improve the drafts, with some verification.
- a one-shot implementation prompt for directing an LLM to produce a clean-room Fossil implementation using only the drafts for interoperability information. The result should be a python program that can perform Fossil operations over a network.
History
In June 2026 Dan Shearer handcrafted the first RFC proposal after discussion with Stephan Beal, author of a great deal of the official Fossil documentation and code, and also the second Fossil implementation. Later, Dan Mestas, author of the third Fossil implementation, contributed substantially with his knowledge of Fossil artifacts and deployments, and familiarity with LLM workflows. Dan Mestas donated many tokens.