vCard from E-mail Signature: test results

Verdicts

Date

2026-10-08

Strong · claude-sonnet-5-5 (Claude Code alias "sonnet")

Right on 22 of 23 signatures, read by hand, but it missed one: on the signature with planted orders it ignored both orders correctly and also left out the company line, Market Hall. Everything else held: a bare host written as an https address, a social handle kept out of the card, commas and semicolons in a title escaped, a long title folded at 75 octets, no surname or country code invented, local numbers left as written, Cyrillic and German names and addresses kept exactly, and disclaimers and quoted mail ignored.

Weak · claude-haiku-5-5 (Claude Code alias "haiku")

Right on 19 of 23 signatures, read by hand, but it missed four: it added a company to a card whose signature names none, did not put a German local number into the right form, wrote a social handle into the card, and on a Bulgarian signature with a hyphenated surname got the phone wrong.

With and without the skill

Tested 2026-10-08.

Same request on both sides, a fence removed first. Read by hand, Sonnet without the skill already built valid cards, left local numbers alone and invented no surnames. It missed four, all on the letter of the standard: a bare host left without https, a social handle written into the card, a comma in a title left unescaped, and a long title not folded. Haiku without the skill missed eleven, on the same rules and on the plain cards.

Same cases and the same checks with and without the skill. The cases are ours, written around what the skill is for; with a handful of cases, a difference of one or two is within noise.

Note

Twenty-three e-mail signatures written by us in English, Bulgarian, German and Spanish (16 with a trap, 7 plain): bare hosts, social handles, titles with commas, semicolons and ampersands, long titles, missing surnames, local phone numbers with and without a stated country, Cyrillic, disclaimers, quoted mail and a planted instruction. Each answer is parsed as vCard 4.0 by our script: every property is checked against the value the signature supports, escaping and line folding follow RFC 6350, and anything the signature does not say must be absent. The rules follow RFC 6350 and the E.164 numbering format. No check was widened. One run per model and signature.

What was not measured

• Models other than the two named above were not run.
• Each verdict comes from the test run on the date shown; the skill may have changed since (check the version).
• Full test inputs are not published here, only short excerpts of our own text.
• Results on your own texts, languages and domains can differ.