Household vinegar is an effective weed killer.
Vinegar only burns the parts of a weed it touches, so it works on tiny seedlings, but bigger and perennial weeds grow back from the roots. It also harms any plant it hits, crops included. The strong "horticultural" kinds can burn skin and eyes. Use it for seedlings in paving cracks. It isn't a garden weed killer.
What is actually known
Household vinegar is about 5% acetic acid, a contact herbicide. It burns only the parts of a plant it touches, fastest in bright sun, and gives excellent control of very small annual broadleaf weeds. It does not move to the roots, so larger and perennial weeds can regrow a week or so later, and it is non-selective, injuring any plant it lands on. Stronger products are more dangerous to the person using them. At 11% acetic acid or more, vinegar can burn skin and cause severe eye injury, and 20-30% formulations call for protective gear. It is most useful for weeds in gravel and on patios and sidewalks. It is not a general weed killer.
The evidence
Evidence: checked against 2 sources in the research-based literature.
The 2 sources
Household vinegar is generally 5% acetic acid
Excellent control when contacting very small annual broadleaf weeds
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Milpa Gardens. “Household vinegar is an effective weed killer.” Evidence grade: Contested. https://milpa.garden/beliefs/vinegar-weed-killer-vinegar-herbicide/
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