Who checks the checker
At the end of a migration somebody signs a piece of paper. The evidence behind that signature almost always comes from the tool that performed the move, because it is the only thing that was watching.
That is not an accusation. A migration tool is built to move things and to tell you how the moving went, and it does that well. But a report by the party that did the work is the party's account of its own work, and no amount of detail changes what it is. When something turns up missing eighteen months later, the question is not whether the report was thorough. It is whether anybody could have checked it.
A migration cannot be verified afterwards
This is the part that surprises people, and it decides everything else about this tool.
Decommissioning the source is the whole point of a migration. Once it is gone, there is nothing left to compare the destination against, so a verification that begins at sign-off is not a verification at all. It is an inventory of the new place, and an inventory cannot tell you what is absent from it.
The comparison needs two reads: one before the move, one after. The first is the only irreplaceable artefact in the process, and nobody can produce it retroactively. A project that did not take one can never be verified, and that is worth knowing at the beginning rather than at the end.
What gets compared, and what each answer is worth
Eight dimensions, and every one of them is published with what it cannot establish. That second column is the reason this exists.
| Dimension | Establishes | Does not establish |
|---|---|---|
| Presence | an item with this identity exists on both sides | that it is the same item, if identity was rewritten |
| Count | how many items each container holds | which ones differ |
| Size | the byte size matches | that the content matches |
| Content | equality, only if hashed on both sides | anything at all, if hashing was not run |
| Authorship | whether the original author survived, or became the migration account | who the author was, once the source is gone |
| Versions | how many versions arrived | whether the ones dropped mattered |
| Permissions | the principals and roles on each side | whether a broader result was intended |
| Sharing links | which existed, and which still resolve | whether anyone was still using them |
A migration report has no second column. It does not need one, because its purpose is to conclude that the migration succeeded.
Three rules the record will not break
An item nobody could read is not an item that went missing. If a folder could not be reached, a file was checked out, or a permission would not resolve, the result is unknown, with the reason and the side it fell on. Reporting it as missing would sound more useful and would be a claim nobody established. Reporting it as fine is worse.
Two files of equal size are not the same file. If content was compared by size alone, the record may say many things but it may never say the content matched. The strongest honest answer is unknown, and the software refuses to write anything stronger.
There is no percentage. No score, no grade, nothing to put on a slide. 96% migrated is what a reader substitutes for the table above the moment it is offered, and the substitution is what destroys the document. There is nothing here to aggregate, deliberately.
What it never does
- It never moves anything. The moment it writes to either side it becomes the producer, and the whole point is gone.
- It never remediates, recommends or ranks. It says what is.
- It never requires us. The record is canonical, digested, and checkable by anyone you hand it to, on their own machine, with no account and no licence.
- It never claims an absence it could not observe.
Where it is
The contract is published and the comparison runs. The collectors that read a real estate are in progress, and this page will say so until they are not.
It is part of the same open source engine as the governance rules, under the same licence, and it inherits the vocabulary: five outcomes rather than pass and fail, coverage stated in words, and evidence that survives the people who produced it.