In the documentation I found the following description for "latestSolidSubtangleMilestone":

The latest milestone which is solid and is used for sending transactions. For a milestone to become solid your local node must basically approve the subtangle of coordinator-approved transactions, and have a consistent view of all referenced transactions.

But I still do not understand this.

  1. What does solid mean?
  2. What is this text trying to explain?

1 Answer 1


The Latest Milestone is the latest milestone you have received from the coordinator.

The Latest Solid Milestone, as the documentation says, is the latest milestone where your node has all transactions that are directly or indirectly referenced by it (called subtangle here). If some transactions are missing, the milestone is not solid and your node is not synced.

Therefore, the LSSM is often used to determinate whether or whether not a node is synced. As it is, as the text states, used to send transactions, an outdated solid Milestone might result in transactions not being approved

  • 2
    I think people might be confused as to what it means, that a solid milestone “is used for sending” transactions. As far as I understand: When you send a transaction, you need to confirm two others. As long as we are having the COO, one of those two transaction hashes to be included, will always be the latest solid milestone. That is, what is meant with “using a solid milestone for sending”.
    – ralf
    Feb 5, 2018 at 21:25

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