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Free Font Repair Tool & Validator

Is your font damaged, malformed or refusing to work correctly? Upload a TTF, OTF, WOFF or WOFF2 font and our free online Font Repair Tool will inspect its internal font tables for structural problems, corrupted references, invalid bounding boxes, checksum errors and other common faults.

The built-in font linter reads the actual binary font tables rather than guessing from how the font renders. Where a problem can be repaired safely, the tool can automatically rebuild the affected data and generate a clean repaired font ready to download.

• ✓ Free to use
• ✓ No registration required
• ✓ Supports TTF, OTF, WOFF and WOFF2
• ✓ Detects structural font errors
• ✓ Automatically repairs supported problems
• ✓ Rebuilds font checksums
• ✓ No fabricated glyph or outline data

Repair Broken and Malformed Font Files Online

Font files are complex binary documents containing dozens of interconnected tables. A font can appear perfectly normal while still containing incorrect checksums, damaged character mappings, invalid glyph references or incorrect metrics that cause problems in browsers, operating systems, design software and font conversion tools.

The uFonts Font Repair Tool & Validator provides a structural examination of TTF, OTF, WOFF and WOFF2 fonts. Rather than simply attempting to open the file, the tool examines the font's internal tables and reports problems that could indicate a malformed or incorrectly generated font.

What Does the Font Validator Check?

The scanner analyses the internal structure of the uploaded font and looks for a range of potential problems.

These include missing required font tables, invalid table relationships, malformed character mappings, incorrect glyph references and bounding boxes that are too small to contain their actual glyph outlines.

For TrueType fonts, the diagnostic engine also examines the relationship between important tables such as glyf, loca, cmap, head, hhea, hmtx, maxp, name, post and OS/2.

This can reveal problems that may not be obvious simply by previewing the font.

Automatic Font Repair

Finding a font error is useful, but fixing it is even better.

When the scanner discovers a problem that can be corrected safely and unambiguously, the Sanitize & Fix option can rebuild the relevant font data automatically.

The repaired font is then rebuilt as a clean font binary with fresh table checksums and a recalculated font-wide checksum.

Repairs are deliberately conservative. The tool will not invent missing outlines or attempt to guess what damaged glyphs were supposed to look like. Problems that cannot be repaired reliably are reported rather than silently modified.

TTF, OTF, WOFF and WOFF2 Support

The Font Repair Tool supports the most common desktop and webfont formats:

TTF (TrueType Font) – Standard TrueType desktop fonts containing quadratic glyph outlines.

OTF (OpenType Font) – OpenType fonts, including fonts using CFF outlines.

WOFF (Web Open Font Format) – Compressed webfonts commonly loaded using CSS @font-face.

WOFF2 – Modern Brotli-compressed webfonts widely used by today's websites.

WOFF and WOFF2 files are decoded so their underlying font tables can be inspected by the same structural diagnostic engine.

Why Do Font Files Become Corrupted?

Malformed fonts can be produced in many different ways. Problems sometimes originate in old font editing software, unsuccessful format conversions, poorly implemented font generators or aggressive font-subsetting tools.

Fonts recovered from websites, PDFs and old software archives can also contain unusual or incomplete structures.

Even a font that renders successfully in one application may fail in another because different font engines tolerate different kinds of malformed data.

Running the font through a structural validator can help identify the underlying problem.

Glyph and Bounding Box Validation

Every TrueType glyph contains information describing the area occupied by its outline. Incorrect bounding boxes can cause glyphs to be clipped or incorrectly handled by strict font renderers.

The uFonts validator calculates glyph bounds from the actual outline data and checks whether the declared bounds are large enough to contain them.

Composite glyphs are handled too. These are characters constructed from other glyphs, such as many accented letters. Their component transformations must be taken into account when calculating the real extent of the character.

Character Mapping Checks

The cmap table connects Unicode characters to glyphs inside the font.

A damaged or badly generated font can contain character mappings that point to glyph IDs that do not actually exist. These dangling references can cause missing characters or unpredictable behaviour in software consuming the font.

The validator checks these mappings against the font's declared glyph count and reports invalid references.

Font Checksum Repair

OpenType and TrueType fonts contain checksums that allow software to verify the integrity of individual font tables and the font as a whole.

When a repaired font is generated, the uFonts repair engine rebuilds the font tables and recalculates their checksums along with the font-wide checksumAdjustment.

This produces a clean binary rather than simply patching the original file.

When Should I Use the Font Repair Tool?

Try the validator if:

• A font refuses to install.
• A font works in one application but not another.
• A converted font behaves incorrectly.
• Characters are missing or clipped.
• A webfont produces unexpected errors.
• You suspect a TTF or OTF file is malformed.
• You have generated or subsetted a font and want to check its structure.
• You want to inspect an old or recovered font before using it.

Simply upload the font to receive a structural diagnostic report. If supported repairable problems are found, use Sanitize & Fix to generate a repaired version.