Google Autocomplete: A Free, Keyless Keyword Research API

Google's autocomplete endpoint at suggestqueries.google.com returns up to 10 suggestions per query without any API key or login. By fanning out with A-Z suffixes, question prefixes, and prepositions, you can generate hundreds of long-tail keyword ideas per seed. The endpoint is rate-limited but works reliably with polite pacing and deduplication.