Compare Family Trees: Diff Two GEDCOM Files Before You Merge

Merging two family trees is one of the most error-prone things a genealogist ever does. A bad merge can fuse two unrelated families into one, attach the wrong children to the wrong parents, and create date contradictions that ripple through every downstream calculation. Once two GEDCOMs are combined, untangling them is exponentially harder than it would have been to compare them carefully first.

GEDminer lets you load two GEDCOM files and compare them across data quality scores, structural metrics, individual counts, sourcing depth and place-name coverage. You see exactly which tree is "stronger" on each axis, where the overlap is, and whether a merge is likely to *improve* your tree or quietly degrade it.

The comparison runs entirely in your browser - both files stay on your device. Use it before importing a tree from a relative, before merging two of your own working files, or just to sanity-check what you're about to commit to.

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How GEDminer solves it

You're about to merge two trees and don't know which is "better".

Side-by-side Tree Health Score comparison shows which tree is stronger on completeness, sourcing and consistency.

Tree Comparison →

You don't know how much overlap there is between two trees.

Comparison surfaces shared individuals using phonetic + fuzzy matching so you can see overlap before merging.

Duplicate Finder →

You suspect an inherited tree has lots of bad data.

Run a full audit on the inherited file in isolation before merging it into your main tree.

Tree Health Audit →

You want to track whether your latest cleanup actually improved the score.

Compare two exports of the same tree (before and after) to see exactly what moved.

Score Comparison →

You're collaborating with a relative on the same family.

Each researcher exports a GEDCOM and the comparison shows where you agree, differ, and complement each other.

Collaborative Comparison →

You want a clean baseline before any further research.

Use the audit results to fix the worst issues in each file *before* merging, not after.

Pre-merge Audit →

Why comparing trees beats merging blind

A blind merge accepts that you will introduce errors - the only question is how many. A pre-merge comparison turns a one-way irreversible operation into an informed decision: which tree wins on each axis, where the overlap is, and where the genuine new information lies.

The time investment is small (the comparison runs in seconds) and the downside avoided is large (untangling a bad merge can cost weeks). For why this matters so much, see our guide on GEDCOM error propagation.

What the comparison shows

Side-by-side metrics for both files:

Tree Health Score - overall and per sub-score (Completeness, Sourcing, Consistency).
Individual count - total, with-vital-dates, with-sources, living vs deceased.
Family count - total, with-children, with-marriage-date.
Generation depth - how far back each tree reaches.
Place coverage - count of distinct standardised places.
Sourcing depth - sources per fact.
Structural integrity - orphan records, broken links, ID collisions.

Use these to decide which tree is the better baseline and which is the supplementary source.

Comparing two exports of the same tree

One of the most useful workflows is comparing your own tree against a previous export - typically your last backup before a cleanup session. The comparison shows exactly which numbers moved, validating that your work actually improved the metrics you intended to improve.

This is particularly powerful for sourcing pushes (where the sourcing sub-score should rise) and for integrity cleanups (where the consistency sub-score should rise).

Privacy: both files stay on your device

Both GEDCOMs are parsed in your browser using Web Workers. Neither file is uploaded. The comparison logic is entirely client-side. The only optional data ever transmitted is the anonymised Tree Health Score for the community percentile, and only if you explicitly opt in.

Step-by-step guides

How to Merge Two GEDCOM Files Without Losing Data

Combining two family trees is one of the most error-prone tasks in genealogy. This guide walks through a safe merge workflow using GEDminer to spot duplicates, conflicting dates, and overlapping branches before you commit.

GEDCOM Error Propagation: How Bad Family Tree Data Spreads

One wrong date, duplicate person, or bad merge can spread through a GEDCOM file and corrupt hundreds of downstream facts. Learn how genealogy errors propagate - and how to audit your tree before importing or sharing.

Finding and Merging Duplicate Individuals

Find potential duplicate individuals in your tree using smart matching, compare their records side-by-side, and learn best practices for merging them.

How to Find and Fix GEDCOM Errors

A practical guide to detecting impossible dates, missing records, duplicate entries, and other data quality issues in your GEDCOM family tree file.

Understanding Your Tree Health and Data Quality Score

Learn how GEDminer evaluates your tree's data quality, what the health score means, and practical steps to improve your tree's completeness and accuracy.

How to Analyse a GEDCOM File Online

A step-by-step walkthrough for uploading your GEDCOM file and getting instant insights into your family tree - demographics, errors, migration patterns, and research priorities.

Frequently asked questions

How do I compare two GEDCOM files?

Load the first file as you normally would, save it to your account if you want to keep it, then load the second file. The My Trees page shows side-by-side metrics for both. The detailed compare dialog opens when both trees have a Tree Health Score.

Does comparing trees actually merge them?

No. The comparison is read-only - it shows you the differences and lets you make an informed decision. Actual merging is done in your main genealogy software, where you have full control over what gets accepted.

Can I compare two exports of my own tree to see what changed?

Yes. This is one of the most useful workflows: export before a cleanup session, do the cleanup, export again, and compare. The score movement validates that your work had the effect you intended.

Will both files be uploaded to a server?

No. Both files are parsed in your browser. The comparison logic runs entirely client-side. Your data does not leave your device.

How does GEDminer detect overlap between two trees?

The duplicate finder uses Soundex phonetic codes plus Levenshtein edit distance against names, vital dates and parent links, with a tunable confidence threshold. Pairs above the threshold are flagged as likely shared individuals.

What if the two trees use different place-name formats?

The location standardiser normalises place names before comparison so "London, England" and "London, Middlesex, England, UK" are treated as the same place where appropriate.

Is there a limit on tree size?

Each file can be up to 150MB. Comparing two very large trees (~200k individuals each) takes longer because both have to be parsed and indexed, but is supported on a modern desktop or laptop.

Can I save both trees in my account?

You can save up to 3 trees per account to a managed cloud database (encrypted in transit and at rest). The comparison view works against any two saved trees, or against a saved tree and a freshly loaded file.

Ready to analyse your tree?

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