Font inspector for Windows

Windows will happily install a font and then let a page fall back to Arial for the one character you needed. An inspector tells you that before your users do.

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What "inspecting" a font means

Table directory - every table in the file with its byte offset and checksum. A missing cmap or loca is why a font renders as boxes.
Metrics - units per em, ascender/descender, x-height, line gap. The numbers that decide whether text lines up with the rest of a design.
Classification and Unicode ranges - what the font claims to cover.
Glyph table - rendered from the real outlines, not from a cached preview image, so what you see is what the file contains.
Coverage check - exactly which code points are missing, grouped by Unicode block. This is the fastest way to answer "does this font have the character I need?"

A five-minute check before you ship a font

Open the font. Read the health report: missing required tables, loca/head consistency, whole-file and per-table checksums, signature presence, variable-font axes.
Run the coverage check against the languages your page actually shows.
Look at the glyph table for the characters that matter - ligatures and diacritics are where fonts quietly fail.
Only then convert or subset.

Reading two fonts side by side

TypeSmith can show two fonts next to each other: metrics, coverage and glyph shapes. That is usually enough to decide which of two similar typefaces will survive the fallback stack on a phone.

Inspection, coverage and the health report are free. Conversion, subsetting, SVG outline export and per-user font install/uninstall are the one-time Pro unlock.

Questions

Does it modify fonts?

No. Inspection is read-only; it writes only the files you explicitly export.

Can it open a font inside a TTC collection?

Yes, TTC files are opened per subfont.

Does it tell me the licence?

It reads the licence bits the font declares in its own tables - which is what you can rely on, as opposed to what a download page claims.