> For the complete documentation index, see [llms.txt](https://gitbook-docs.coinmetrics.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://gitbook-docs.coinmetrics.io/index-data/coin-metrics-bletchley-indexes-cmbi/fork-legitimacy-framework.md).

# Fork Legitimacy Framework

Cryptoasset networks operate programmatically, where transaction validity is determined by the underlying code upon which the blockchain runs. This code is governed by a set of “consensus rules”. There are two types of forks that cryptoassets can undergo:

1. If a change in consensus rules does not require nodes to implement software changes in order to be compatible with the new set of rules (i.e. backwards compatibility), this is known as a soft fork.
2. If a change in consensus rules requires nodes to implement new software in order to remain compatible with the new set of rules, this is known as a hard fork.

This framework only considers forks of cryptoassets with Proof-of-Work consensus mechanisms.

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