You'll need: FontCreator (Windows and macOS), a font project nearing completion, a few diacritic-heavy and multi-language test glyphs, and a web browser for the web-font preview.

You've drawn the glyphs, set the metrics, and built your composites. Before you ship your TTF, OTF or WOFF2, it's worth one disciplined QA pass to validate and test the font. This tutorial walks three complementary surfaces in the order a designer actually uses them inside the font editor: first you catch geometry problems with the Font Validation wizard (the built-in font validator), then you confirm your OpenType layout behaves with Font Inspection and the OpenType Designer, and finally you type in real apps with the Test Desktop Font and Test Web Font tools.

Surface 1 — Run the Font Validation wizard

The Font Validation wizard lives on the Font menu as Validate…. It validates every glyph, flags common problems, and where possible points you straight to the offending glyph, contour, and coordinate. It can also fix many issues for you.

1. Open your font and choose Font → Validate… to open the Font Validation Wizard.
2. On the tests page, tick the checks you want to run. The wizard groups them by problem type.
3. Run the validation and review the reported items.

What it checks:

• Outline issues — duplicate contours, contours with one or two points, contours with incorrect direction (filled contours must run clockwise; counters run counterclockwise), and intersecting coordinates (self-intersections and crossing contours).
• Component issues — empty components, overlapping components (intersecting glyph members), and duplicate components (two or more identical members).
• Point issues — redundant points, duplicate knots (two adjacent points at the same coordinate, one on-curve and one off-curve), suspicious points (likely misplaced), and off-curve extreme coordinates (off-curve points falling outside the bounding box).
• Variable-font checks — interpolation issues (mixed-up contours or members, mismatched start points, different contour directions) and unbalanced components (a member scaled or rotated differently across masters, which FontCreator converts to simple contours on export).

For off-curve extremes, the wizard can act for you: with local detection enabled, the Add on-curve extremes button on the Validation panel inserts the missing extreme points. Use the panel's jump-to-offender behavior to step from a reported issue directly into the glyph and the exact coordinate.

Tip: Tune which extremes are flagged in Tools → Options → Validation, under the Off-curve extreme coordinates group — choose Global detection or Local detection.

Watch out: Overlapping contours and components are tolerated by most modern rasterizers, but older PostScript Level 2 drivers don't support them. If you care about legacy output, resolve overlaps rather than ship them.

Note: Auto-fix is convenient, but review each change. "Wrong direction" on a deliberately reversed counter, for example, is a fix you may not want.

Surface 2 — Proof OpenType features with Font Inspection

Clean outlines don't guarantee correct shaping. Next, confirm your substitutions and mark positioning work on the glyphs most likely to break: accented and composed characters.

1. In the font overview, select a batch of diacritic-heavy glyphs — accented Latin, marks, and any composed forms.
2. Press P to send the selected glyphs to the Preview panel.
3. Toggle the layout features that drive composition and positioning — ccmp, mark, and mkmk — and watch how the glyphs reflow.
4. Open the OpenType Designer and run the shaping engine to trace what's happening step by step. Look for substitutions that don't fire and composite members that go missing.

If a mark lands in the wrong place or an accented form doesn't compose, the shaping trace is where you'll see which rule failed. For a deep walkthrough of reading that trace and fixing broken lookups, see Debug OpenType Features with Font Inspection (linked below).

Tip: Test the same string with a feature on and off. If nothing changes when it should, the lookup probably isn't being reached.

Surface 3 — Test on the desktop and the web

Now type in real software. FontCreator lets you do this without a permanent install.

Test Desktop Font

Test Desktop Font (ttf/otf) (Font menu) registers your font temporarily so you can use it in other applications — a word processor, a browser, a design tool — without installing it system-wide. The registration goes away when you're done, so you can iterate quickly.

1. Choose Font → Test Desktop Font (ttf/otf), or press F5.
2. Switch to another app and select your font from its font list.
3. Type your test strings and check rendering at several sizes.

Test Web Font

Test Web Font (woff/woff2) generates a local web page so you can test the font — and its OpenType layout features — in a browser. Choose Font → Test Web Font (woff/woff2) or press Ctrl+F5. If layout features are present, the generated page gives you default, on, and off buttons on the right to toggle each one.

Note: On the web, ligatures are disabled as soon as you set a non-default letter-spacing (for example letter-spacing: 0.1em;). If your ligatures "stop working" in a layout, check the spacing first.

Tip: You can edit the predefined preview text via the FontCreator Data Files, so your web preview always shows the strings you care about.

What to type

Use strings that exercise the whole font, not just lowercase:

• The full alphabet, upper and lower case
• Accented forms: à á â ä ã å ç è é ê ë ñ ö ü and composed cases like Ǻ
• Figures and math: 0123456789 +−×÷=%
• Punctuation and symbols: . , ; : ! ? ' " ( ) [ ] / & @ — –
• Kerning pairs: AV To Yo We LT P. F, r. va
• Language samples (a sentence each) for the scripts you support
• Vietnamese stacked diacritics: ế ề ễ ộ ợ ự — these stress your accent placement hardest

Missing-codepoint check: Paste a sample covering every codepoint you claim to support and look for .notdef boxes. Anything that renders as a box is unmapped or undrawn.

Vertical-metrics / clipping check: Render tall accents and stacked Vietnamese marks at large and small sizes. If tops or bottoms are clipped in real apps, revisit your vertical metrics (ascender/descender and line-gap) rather than the glyphs.

Pre-release checklist

• Font Validation run with all relevant tests; reported issues fixed or consciously accepted
• Contour directions and overlaps resolved (especially for legacy targets)
• Variable-font interpolation and unbalanced-component checks clean
• ccmp / mark / mkmk verified on accented and composed glyphs
• Broken substitutions / missing composite members traced in the OpenType Designer
• Test Desktop Font typed in at least two real applications
• Test Web Font checked with feature buttons (default/on/off)
• Test strings cover alphabet, accents, figures, punctuation, kerning, language samples
• No .notdef boxes for any claimed codepoint
• No clipping on tall accents or Vietnamese stacks
• Final external pass with Font Bakery and/or OpenType Sanitizer (OTS)

External validation

That last external pass is worth the few extra minutes: a second font validator catches table-level and spec-conformance problems that an in-editor preview can't, and these tools are what many distributors run on intake — for desktop TTF/OTF and web WOFF2 files alike. Useful external validators:

• Font Bakery — a command-line suite that runs hundreds of conformance checks against TTF and OTF files.
• OpenType Sanitizer (OTS) — the same sanitizer browsers use to accept or reject web fonts; it parses and re-serializes the font and reports any table it considers unsafe, which is exactly what gates a WOFF2 web font from loading.
• FontDrop — a browser-based inspector: drag a font in to read its tables, features, and metadata with no install.
• Microsoft Font Validator — a long-standing tool that produces a detailed table-by-table conformance report.

Frequently asked questions

Which font validator should I use? Start with FontCreator's built-in Font Validation wizard to catch geometry, component, point, and variable-font problems. Then run a final external pass with a second font validator — Font Bakery, OpenType Sanitizer (OTS), FontDrop, or Microsoft Font Validator — to catch table-level and spec-conformance issues an in-editor preview can't.

What does OTS check? OpenType Sanitizer (OTS) is the same sanitizer browsers use to accept or reject web fonts. It parses and re-serializes the font and reports any table it considers unsafe — which is exactly what gates a WOFF2 web font from loading.

How do I test a WOFF2 web font in a browser? Choose Font → Test Web Font (woff/woff2) or press Ctrl+F5. FontCreator generates a local web page so you can test the font and its OpenType layout features in a browser, with default, on, and off buttons to toggle each feature.

What to read next

• Debug OpenType Features with Font Inspection — read the shaping trace and fix lookups that don't fire.
• Export a Font (Export Fonts Correctly) — choose the right format and settings once your font passes QA.