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When two sources disagree, which one is lying?

The reconciliation view compares the budgeting app against itself. The next step is a bank-side feed through a second API, landed the same way, so drift has an independent referee.

StatusPlanned · 2027
Depends onAPI access to the bank aggregator; the landing pattern from the finance ETL
PatternAppend-only raw landing, pure SQL transforms, a cross-source balance view

Video · 60 sec Why one source of truth is never enough

Placeholder Talking head: the drift story from part 5, then the question of what you check against when the app itself is wrong.

The design

Land the second feed exactly like the first: raw JSON in an append-only table, transforms in SQL, soft deletes, a cursor per endpoint.
One view joins account balances from both sources by a mapping table and reports the difference with a tolerance.
The weekly action check reads that view. Drift between the sources becomes an item with the fix attached.

Two landing paths, YNAB and a bank aggregator, converging through a mapping table on one balance view with a tolerance band. — Diagram of two landing paths converging on a reconciliation view, with the mapping table in the middle. Also as a square.

What I expect to learn

How often the two disagree, who is usually right, and whether the second source earns its monthly fee.

Write to me

I built this for a household. Imagine it pointed at your company.

Fractional CTO and CFO engagements start with a short call. No deck required, no pitch either. Bring the number you do not trust.

Tell me what is stuck