You'll need: FontCreator (Windows and macOS), a finished TTF or OTF you have permission to modify, and a few minutes to set up a safe workflow before you touch a single outline.

Tweaking a font someone else built — or one you exported months ago — is one of the most common things designers do. Maybe a single glyph needs redrawing, an a needs a friendlier terminal, or you want to nudge the spacing. The danger isn't the edit itself. It's everything around the edit: the OpenType features, the kerning, the line spacing and the naming that a finished font carries quietly in the background. Break one of those and the font still opens — it just stops behaving the way it used to.

This guide is the safe-editing workflow. It keeps your change small and your font intact.

Step 1: Check you're allowed to edit it

Before anything else, confirm you actually have the right to modify the font.

• If you made it, you're fine.
• If it's a commercial or third-party font, read its license. Many licenses permit personal tweaks; some forbid modification entirely; some allow it but bar redistribution of the modified file.
• Fonts also carry embedding permissions inside the file (the fsType field). A font marked as not editable is signalling that the foundry doesn't want it modified for embedding. Respect that signal.

> Note — This is general guidance, not legal advice. When in doubt about a specific license, ask the foundry or a lawyer. The technical workflow below is the same regardless; the question of whether you may edit is separate from how.

Step 2: Open the font — and work on a copy

Open your TTF or OTF with File → Open as usual.

The single most important habit: never edit your only copy. Before you change anything, save the project under a new name (FontCreator's native project file) so the original binary stays untouched. If an edit goes wrong, you delete the project and start again from the pristine original.

> Tip — Treat the original TTF/OTF as a read-only master. Make a dated backup folder, drop the untouched original in there, and do all your work on a copy. You'll thank yourself the first time an experiment goes sideways.

What can break when you edit a finished font

A finished font is more than a set of outlines. Editing one glyph can ripple into systems you weren't even looking at. Here's what's at risk:

• OpenType layout features — ligatures, alternates, small caps, fractions, contextual rules. These are written against specific glyphs by name. Delete or rename a glyph a feature references and the rule silently breaks.
• Kerning — pair adjustments are stored against glyph pairs (or classes). Remap or remove a glyph and its kerning goes with it.
• Vertical metrics / line spacing — ascender, descender, line gap and the related table values control how text stacks. Touch them carelessly and every paragraph set in the font re-flows.
• Hinting — instructions that sharpen rendering at small sizes are tied to a glyph's exact point layout. Redraw the outline and the old hinting no longer matches.
• The name / family table — the font's family name, style, version and unique identifiers. Change these without thought and the OS may treat your edit as a different font, or refuse to replace the original.
• Glyph mapping (cmap) — which character maps to which glyph. Break the mapping and characters stop showing up.

> Watch out — The font will still open and export even after you've broken one of these. The damage shows up later, in the app that uses the font: a ligature stops firing, a small-cap goes missing, lines suddenly sit too far apart. That's why the validation and proofing steps at the end of this guide aren't optional.

FontCreator's advantage: it keeps the intelligence intact

Here's the good news. FontCreator was built to let you edit glyphs without discarding the OpenType layout intelligence already in the font. When you open a finished font and redraw an outline, the features, classes and kerning that reference that glyph stay in place — you're editing the shape, not unwiring the logic.

That means the riskiest part of font editing — losing all your features the moment you make a change — simply doesn't happen here for ordinary outline edits.

Where you do need to be careful is anything that changes a glyph's identity or existence:

• Renaming a glyph that features or kerning reference.
• Remapping a glyph to a different codepoint.
• Deleting a glyph that other glyphs (composites) or features depend on.

Any of these can leave a feature, a composite, or a kerning pair pointing at something that's no longer there.

> Tip — Edit shapes freely; treat names, codepoints and deletions as the dangerous operations. If you must rename or remove a glyph, search the font's features and composites for references first, and update them in the same session.

Step 3: Make your edit, minimally

Keep the change as small as the goal allows.

• Redrawing an outline? Edit the points directly in the glyph editor. The glyph keeps its name, codepoint, anchors and feature references.
• Adjusting spacing for one glyph? Change its side bearings rather than reaching for a font-wide metrics overhaul.
• Swapping a shape? Replace the outline, but keep the glyph's name and mapping so everything that references it keeps working.

The narrower the edit, the smaller the surface area for something elsewhere to break.

> Note — If your change is genuinely font-wide (re-spacing every glyph, restyling a whole script), that's a bigger project than "editing safely" — and it deserves the dedicated metrics and spacing workflow rather than a quick tweak.

Step 4: Re-validate before you trust it

Once your edit is in, run FontCreator's validation pass. This is your first line of defence — it catches structural problems (missing references, broken composites, mapping issues, contour faults) before they reach a real application.

This is a whole topic of its own, with a checklist of what to look for and how to clear each report. See Test & Validate Your Font below — don't skip it after an edit, even a small one.

Step 5: Proof the features

Validation checks structure; it doesn't tell you whether your features still do the right thing. For that you need to proof them — type real text and confirm that ligatures, alternates, small caps and the rest still fire as expected, especially anything that involves the glyph you just edited.

FontCreator's feature inspection tools let you watch substitutions happen and trace why a rule did or didn't apply. If a feature broke because you renamed or remapped a glyph, this is where you'll catch it. See Debug OpenType Features with Font Inspection below. Open the OpenType Designer from the Font menu, and within that windows, click the Proofing toolbar icon.

Step 6: Check vertical metrics consistency

If you edited only outlines, your vertical metrics are probably untouched — but verify it anyway, because inconsistent line-spacing values are one of the most common reasons an "edited" font suddenly stacks text differently from the original.

The goal is consistency: the ascender, descender, line-gap and related table values should agree with each other and (ideally) match the font you started from, so paragraphs don't re-flow. The dedicated guide walks through exactly which values to check and how they interact — see Font Metrics – Vertical Line Spacing below.

Step 7: Re-export with the right settings — and the right name

The final trap is naming. If you want your edit to replace the original, the family and style identity must line up so the OS recognises it as the same font. If you want it to coexist as a separate font, you must give it a distinct family name — otherwise the two collide and the OS may pick one unpredictably.

Decide which you want, set the family details accordingly (see Font Family Settings below), then export with the correct format and options. Export is its own workflow — outline format, naming, open-contour handling and more — covered in Export a Font below.

> Watch out — Re-exporting a TTF over the original filename does not automatically replace it in the OS. The OS keys on the font's internal family/unique names, not the filename. Get the naming right, or you'll end up with a confusing "two fonts, same name" situation on your system.

Troubleshooting

Frequently asked questions

Will editing one glyph wipe my OpenType features? No. For ordinary outline edits, FontCreator keeps the existing layout features, classes and kerning intact. Features only break if you change a glyph's identity — its name, codepoint, or existence — in a way the features still reference.

Can I edit a commercial font I bought? Only if its license permits modification (and, if you plan to share the result, redistribution). Check the EULA and the font's embedding permissions first. This guide covers the how, not the legal whether.

Should I edit the TTF directly or save a project first? Save a project under a new name and keep the original binary as an untouched master. Always work on a copy so a bad edit is recoverable.

My edited font won't replace the original on my computer — why? The OS identifies fonts by their internal family and unique names, not by filename. To replace the original, the naming must match; to keep both, the names must differ. Set this deliberately before exporting.

Do I need to re-hint after redrawing a glyph? If you changed the outline's points, the old hinting no longer matches. Either re-hint that glyph or let the export step apply auto-hinting.

Is it safe to delete glyphs I don't need? Only after checking that no feature, composite or kerning pair depends on them. Validation will flag dangling references — run it after any deletion.

What to read next

• Test & Validate Your Font — the validation checklist to run after every edit.
• Debug OpenType Features with Font Inspection — confirm your features still fire correctly after editing.
• Export a Font (Export Fonts Correctly) — the right format and settings when you re-export.
• Font Metrics – Vertical Line Spacing — keep line spacing consistent so text doesn't re-flow.
• Font Family Settings — name your edit to replace, or coexist with, the original.