Guides

Data mapping guides: the document, the process, the failure modes

Everything here is written from building a product whose worst outcome is a confident, wrong mapping — so the guides say plainly what a mapping document is, how one gets made, and where the process actually breaks. No listicles, no padding.

Updated August 2026

In reading order below. These pages are explanation — the unedited output they describe is published separately as worked examples.

What is a source-to-target mapping (STTM) document?Definition

The definition, precisely: one row per destination field, stating source, rule, evidence, and open questions — plus one real populated row and the three things an STTM is not.

How to create a data mapping documentHow-to

The columns that keep the document honest, the six steps that produce one, and two real rows from a published run — a checkable mapping and an honest gap.

Source-to-target mapping in Excel — and where spreadsheets breakFailure modes

Excel is the right review medium and the wrong system of record: the five ways workbooks break in review, and the round-trip rules that survive them.

LLM data mapping: confidence, evidence, and knowing when to abstainEngineering notes

Why confidence scores alone mislead, why a suggestion that rests on a rule needs the verbatim line behind it, and why abstention must be a first-class output.

The deliverable every guide circles back to is the same one: a source-to-target mapping document a reviewer can actually check. The guides describe it; the template and the examples are it.

The layout every guide describes ships as a free source-to-target mapping template; to see it filled in by a real run, start with the Salesforce → HubSpot contact mapping.
Draft one from your own specs — freeOr walk a worked sample first