GEDCOM viewer: open a .ged family tree and walk it, nothing uploaded

What it shows

What the file is. The program and version that wrote it (Family Tree Maker, RootsMagic, an Ancestry export…), the GEDCOM version, the character set, the submitter, the export date, and how many people, families, sources, notes and media references it holds.
Everyone in it. A list of every person with sex, birth and death date and place and their GEDCOM ID. Search by name, place, year or ID; accents are ignored, so dvorak finds Dvořák. Sort by surname or birth date. Save the whole list as a CSV for a spreadsheet: name, given names, surname, sex, birth and death date and place, father, mother, spouses and number of children.
One person at a time. A family view with the parents above, the person and their spouses in the middle and the children below; tap anyone to move to them. Below it, each marriage with its date and place, every event and fact (birth, baptism, census, occupation, residence, emigration, burial and the rest) with its date, place, age, cause and the source and page cited for it, and every note.
Ancestors and descendants. Up to ten generations each way. Ancestors are numbered the standard Ahnentafel way (father 2, mother 3, father’s father 4…), and someone reached through two lines, as when cousins married, is marked rather than repeated. Descendants are numbered 1.1, 1.2, 1.1.1 to show who descends through whom.
Problems, each in one plain sentence. Someone born after their own child, a death recorded before the birth, a parent under 12 at a child’s birth, a child born after its mother died (or more than a year after its father died), a lifespan over 120 years, two records sharing one ID, links to records that are not in the file, and links recorded at one end only.
Media references. The photo and document file names the tree mentions, and who they belong to.

Versions, dates and character sets it reads

The reader was written for this page from the GEDCOM 5.5 and 5.5.1 specifications, FamilySearch’s GEDCOM 7.0 and the ANSEL character chart, with no genealogy program’s code.

ANSEL. Many trees from Family Tree Maker, PAF and Legacy are written in ANSEL, where an accent comes as its own byte before the letter it sits on: ANSEL writes Dvořák as Dvo, E9 (caron), r, E2 (acute), a, k. Programs that read such a file as Latin-1 show “Dvoérâak”. This page joins each accent to its letter, Unicode style, so names come out right, including Ł, Ø, Þ, ß and the rest of the ANSEL letters.
UTF-8, UTF-16 and the old sets. The CHAR line of the header decides: UTF-8, UNICODE (UTF-16, with or without a byte-order mark), ASCII, ANSI (Windows-1252), IBM PC and Macintosh. GEDCOM 7 files are always UTF-8. When a file’s bytes contradict its CHAR line, the page says what it did instead.
Long notes. GEDCOM splits long text over CONC lines (joined with nothing between them) and CONT lines (joined with a line break); both are put back together, even when the split falls inside an ANSEL accent and its letter.
Dates as genealogists write them. ABT 1855, BEF, AFT, BET 1910 AND 1915, FROM 1900 TO 1910, CAL, EST, INT with its phrase, dual years such as 11 FEB 1749/50 (read as 1750, the modern year) and B.C. dates are shown in words and used in the checks. French Republican and Hebrew calendar dates are named and shown as written, but not converted, so the checks leave them out.
Zipped trees. A GEDCOM 7 .gdz (a ZIP with gedcom.ged at the top, beside its media) or a .zip with a .ged inside is unpacked in the tab. Its media files are matched against the names in the tree, so you see which ones are really there.

What this cannot do

Edit or merge trees. It only reads. Nothing in the file can be changed, corrected or merged with another tree, and it does not write a .ged back. Make changes in a genealogy program, then open the new export here.
Show the photos. A .ged names its pictures (FILE photos/grandma-1920.jpg) but does not contain them. They are listed as file names only. In a .gdz the files are present and marked as such, but not shown.
Draw a chart. There is no fan chart, pedigree poster or printable family tree diagram: the family view shows one generation above and below, and the ancestor and descendant lists are text.
Check the truth. The checks only test whether the file agrees with itself. A wrong but possible date, two people merged into one, or a made-up ancestor passes. Dates with ABT, CAL or EST are given two years of slack either way, and only problems the dates make certain are listed.
Read LDS ordinance details, source images or every custom tag. LDS ordinances appear as events with their dates; program-specific _TAGS are shown only when they carry a date or a place. Repositories are named on the sources that point to them, not listed on their own.

Getting the .ged file

Ancestry: Trees › Tree settings › Export tree. Ancestry builds the file, then offers Download your GEDCOM file. Photos and stories are not included.
MyHeritage: Family tree › Manage trees › Export to GEDCOM. MyHeritage e-mails a link when the file is ready.
FamilySearch: FamilySearch does not export its shared Family Tree as GEDCOM from the website; programs certified to sync with it (RootsMagic, Ancestral Quest) can download your branch and export that.
Desktop programs: Family Tree Maker: File › Export. RootsMagic: File › Export. Gramps: Family Trees › Export, then GEDCOM. Legacy: File › Export › GEDCOM File. Choosing UTF-8 rather than ANSEL, where offered, gives a file every program reads the same way.

Useful to know about GEDCOM files

What the lines mean: Every line is a level number, an optional ID in at-signs and a tag: 0 @I12@ INDI starts a person, 1 BIRT a birth under them, 2 DATE 12 MAR 1850 its date. Families are separate FAM records that point to a husband, a wife and children by their IDs, and each person points back with FAMC (child of) and FAMS (spouse in).
Why names look garbled in some programs: The usual cause is ANSEL read as if it were another character set, or a UTF-8 file whose header still says ANSEL or ANSI. This page shows which set it used and why; if the names look right here, re-export from the original program in UTF-8 before importing elsewhere.
Why “broken links” appear: Exporting part of a tree (one branch, or living people left out for privacy) often leaves pointers to people or families that were not exported. The list names each one, so you can tell a privacy-trimmed export from a damaged file.
Private people: Some sites and programs replace living people with “Living” or “Private” on export, or leave them out. They still appear in the list and in their families, with no dates.