Free worked exercise · Original synthetic data

Compare repeated CSV exports when row order and IDs need separate checks

Match a stable ID first, then compare the selected fields. This example includes a changed plan, a repeated ID and an added record.

Run the synthetic proof

Not run yet. Supplied synthetic fixtures only.

No account or payment needed. This exercise sends no input-upload requests and stores no inputs. Normal host access logs may exist.

Inspect the exports

Baseline: record_id,name,plan
001,Ada,start
002,Lin,pro
003,Mira,start
003,Mira,pro

New: customer_id,display_name,tier
002,Lin,pro
001,Ada,pro
003,Mira,pro
004,Bo,start

Choose the mappings

In the complete free browser tool, paste both files and click Read columns →. Choose record_id and customer_id as the matching keys. Under Fields to check, select the plan checkbox and map it to tier. Leave name unchecked and keep default normalization. Click Compare exports →. The names are deliberately outside this check.

Expected classifications

changed: 1       ID 001, start → pro
unchanged: 1     ID 002
ambiguous: 1     ID 003, two baseline records
only_left: 0
only_right: 1    ID 004

The duplicate group stays ambiguous. ID 001 retains its leading zeros. Row reordering alone does not create a field change.

Record the scope

The complete free browser tool can export reports. Matching selected fields does not prove that unchecked columns or business rules are correct. Record mappings and unresolved duplicate groups before a release decision.

Understand the small local sample

The download checks only its supplied simple unquoted CSV fixtures with a single-key example. It rejects quoted input and is not a general parser or the paid toolkit. Use the complete browser tool or a suitable parser for general CSV.

Free alternatives exist

csv-diff supports key-based comparison. CSV-Diff Report already offers file/directory checks and readable reports. Judge whether this kit’s worked setup and examples save useful effort.

Download and reproduce

Download the free exercise ZIP

Extract the ZIP and run with Node.js 22+:

node run.mjs
node exercise.test.mjs

No npm install or API key. Read the README and license before adapting.