Font coverage: does this font have glyphs for this text, and does it fit the box

$0.005 USDC per call · Business, finance and compliance · POST /api/v1/font-coverage · Id font-coverage

Reads a TrueType or OpenType font you supply as base64 (up to 2 MB) and a text of up to 5000 characters, for an agent about to render text in a fixed font: lists every code point with no glyph in the cmap (formats 4 and 12) and sums the hmtx advance widths to test a width in pixels. Every offset is bounds-checked. It does not apply kerning, ligatures or shaping (combining marks and complex scripts make the width check unknown), does not read WOFF, WOFF2 or font collections (unsupported), and does not render the font.

What you get

Catches the tofu boxes and overflowing labels before a design, PDF or image is generated with the wrong font.

Call it

Send the JSON body below to https://agents.writerslogic.com/api/v1/font-coverage. An unpaid request answers 402 with the price and how to pay; a request that fails with a 5xx status is not charged.

curl -i -X POST https://agents.writerslogic.com/api/v1/font-coverage \
  -H 'content-type: application/json' \
  -d '{"fontBase64":"AAEAAAAFAAAAAAAAY21hcAAAAAAAAABcAAAARGhlYWQAAAAAAAAAoAAAADZoaGVhAAAAAAAAANgAAAAkaG10eAAAAAAAAAD8AAAAFG1heHAAAAAAAAABEAAAAAYAAAABAAMAAQAAAAwABAA4AAAACgAAAAAAAABBAEIAQwDp//8AAABBAEIAQwDp////wP/A/8D/GwABAAAAAAAAAAAAAAABAAAAAQAAAAAAAF8PPPUAAAPoAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAMg/zgAWgAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAFAfQAAAJYAAACvAAAAyAAAAImAAAAAFAAAAUAAA==","text":"ABC é","fontSizePx":10,"maxWidthPx":100}'

Input

Field	Type	Required	Description
`fontBase64`	string; length 8..2796204	yes	Base64 of a .ttf or .otf file (sfnt, not WOFF).
`text`	string; length 1..5000	yes
`fontSizePx`	number; 1..2000	no	Needed for a width check.
`maxWidthPx`	number; 0..100000	no	Box width; the widest line (split on \n) must fit.

Example request body

{
  "fontBase64": "AAEAAAAFAAAAAAAAY21hcAAAAAAAAABcAAAARGhlYWQAAAAAAAAAoAAAADZoaGVhAAAAAAAAANgAAAAkaG10eAAAAAAAAAD8AAAAFG1heHAAAAAAAAABEAAAAAYAAAABAAMAAQAAAAwABAA4AAAACgAAAAAAAABBAEIAQwDp//8AAABBAEIAQwDp////wP/A/8D/GwABAAAAAAAAAAAAAAABAAAAAQAAAAAAAF8PPPUAAAPoAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAEAAAMg/zgAWgAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAFAfQAAAJYAAACvAAAAyAAAAImAAAAAFAAAAUAAA==",
  "text": "ABC é",
  "fontSizePx": 10,
  "maxWidthPx": 100
}

Result

The response is { "data": ..., "_provenance": ... }. data carries these fields; _provenance is a signed W3C Verifiable Credential with a C2PA-style manifest, checked free at POST /api/v1/verify-provenance.

Field	Type	Required	Description
`status`	string; one of "pass", "fail", "unknown", "unsupported"	no	pass: every rule held. fail: a rule was violated (see witnesses). unknown: the input lacks the evidence to decide. unsupported: outside what this engine covers. Missing evidence is never a pass.
`font`	one of	no
`requestedCodePoints`	integer	no	Distinct non-newline code points in the text.
`coveredCodePoints`	integer	no
`missing`	array<object>	no
`missingTruncated`	boolean	no
`width`	one of	no
`witnesses`	array<object>	no
`versions`	object	no	Every semantic dependency of this answer (engine, tables and their as-of dates, tokenizer, calendar, rounding profile).
`limits`	array<string>	no
`deterministic`	boolean	no	Always true: pure code, no model.

Pay and connect

Available through: x402 (USDC on Base), MCP. MCP clients reach it through the identifier-text-kit package.

Machine-readable

This agent as JSON (schemas, example, OpenAPI operation)
Free signed sample response
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