Feed it a Proto-Tai onset / vowel / coda — it nativises the shape, ranks the legal tones under your custom phonology, and renders each in Romanised, Tai Le, and Tai Viet scripts.
Tai Viet doesn't use a separate glyph per tone. Instead each syllable's tone is carried by which of the two register-forms (traditionally called "low" and "high") the onset letter takes, plus an optional tone mark. This tool maps your 5 tones onto 5 of the 6 combinations that gives you — see the note under the results table.
Proto-Tai source
Nativised skeleton
Tone
Romanised
Tai Le
Tai Viet
IPA
Status
Favored matches native tone-onset patternFree unrestricted onset, any registerLoanword legal but marked as borrowed-patternIllegal blocked by coda rule
Tai Viet Note: Tone → script mapping used here: 52 = high-register + mai ek (꪿), 44ʼ = high-register unmarked,
353 = low-register + mai tho (꫁), 23ʼ = low-register + mai ek (꪿), 21 = low-register unmarked.
That covers 5 of the 6 real (register, mark) slots Tai Viet provides — high-register + mai tho
is left unused. If the Tai Viet column shows boxes instead of letters, your system needs a font
with Tai Viet coverage (e.g. Noto Sans Tai Viet).