Via FMP documentation
"We are the most accurate financial data API out there. To make it simple we are a free stock API | historical data API | financial statements API We update our financial statements every 10 minutes every statement is audited, standardized, and up to date. We cover NYSE, NASAQ, AMEX, EURONEX, TSX, INDEXES, ETFs, MUTUAL FUNDS, FOREX and CRYPTO. We have real time stock price, we cover the fundamental data part of the stocks via providing the income statement, balance sheet statement and cashflow statement quaterly and annually."
My opinion
Financial Modeling Prep fetches their data directly from SEC.gov and is consistently updated as noted here. Highly recommend you check them out and support them however you can, in my experience amazing API's to fundamental data like this don't stay free for long, just look at https://intrinio.com/, yahoo finance fundamentals, and google finance fundamentals...both of which appear to be making a return in late 2019
Finviz does not provide any documentation about their api.
My opinion
Cool things can happen if you don't look at their robots.txt ....
Yahoo finance does not provide any documentation about their api.
My opinion
Arguably the most used free web api to historical stock data in the programming community over the past 2 decades (2020)!!!
Via OTC Markets
Free data via here and FAQ for paid data via here
My opinion
Overall a great free resource for getting quotes and other information regarding OTC stocks....Who cares about OTC stocks anyways I'm not interested in buying your penny stock guru course.
My opinion
recently changed their api
Via StockPups Blog August 18, 2019
"We've just updated the site with the data from the latest quarterly filings. Going forward, we plan to reduce the universe of companies that we update on a regular basis. Our website is free, and we need to be mindful of our time allocation."
"All of the current historic data on StockPup.com will remain available. We will continue to regularly update a short list of companies that are of interest to us, e.g. as potential long-term value investment opportunities. If there are specific companies that you would like covered, let us know, and we will consider adding them. You can do so by commenting on this post, or on Twitter."
My opinion
Another amazing resource for fundamental data, dating back the furthest of any of the api's in this list. I assume they have a somewhat manual process to update this data. Appears they are ramping down on updating all of the data, recommend reaching out directly via their twitter if there is any data you would like to see updated.