Are there any sources of OHLC data to download/access

I am writing my own indicator using tradingView script but the limitation is that I need to view each chart to see the indicator. The ideal would be that I have a program/script… that can simply access the opening/high/low/close data for all of the companies on my watch list and generate alerts for me if it thinks there is a buy/sell event. Has anybody done anything similar or are there any sources/api to get the data or any systems (like tradingview) where you can run a script against a watchlist (rather than just one company at a time)

Have a search on Github. People on there get up to that sort of thing. I saw an old thread where a guy was doing algo trading - using T212.
I imagine there’s a load of stuff for the standard charts - MT4,5.