Comparing the best free financial market data APIs

Start here if you are looking to analyse financial market data — for stock markets or crypto, as a data scientist, trader or investor.

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Few things are as inextricably linked in our world as financial markets and data. The entire function of financial markets is based on its participants acting on available information and knowledge synthesised from said information; the objective being to buy or sell an asset at a price that they believe is favourable.

This mechanism sets market prices, which in turn imbues markets with another key property —that of a source of data. Regardless of the validity of the efficient market hypothesis, and objective correctness of the price, few things capture the collective sentiment as well as market data does.

Furthermore, granularity of available data has increased over time to now capture individual sentiments as well as those of the collective. The result is that there are few parallels for any data sources this rich, this extensive and with so much history as markets.

Photo by Aditya Vyas on Unsplash

The New York Stock Exchange, for instance, has been around since 1792(!), and these days just the major exchanges like the NYSE in the United States are said to generate approximately 30 billion market events a day on average.

Given the large sums of money involved in these markets, and the constant cat and mouse game of seeking an edge, the quest for more and better data is not surprising.

And while the markets these days derive a healthy income by selling its data products, there still remain numerous excellent, free entry points to the field of market data analysis. Some of these APIs also provide information on crypto assets as well as from stock markets.

So in this article, I compare a few of the top financial market data APIs’ free tiers. I hope you find them useful.

APIs compared — Overview

IEX Cloud

IEX is a startup stock exchange whose co-founder Brad Katsuyama was made famous by Michael Lewis’ book Flash Boys (Amazon link)

The value proposition of IEX is that it aims to be an exchange “eliminating some of the industry’s worst practices” (article on the Verge). IEX Cloud (website) is the data API arm of IEX, and offers a free tier as below:

IEX Cloud free tier (as of 9/Mar/2020)

Tiingo

They have been around since 2014 (see this discussion on HackerNews from 2015), and if nothing else, having survived for this long is probably a good sign for its reliability and viability.

Their free tier feature outline is captured here:

Tiingo free tier (as of 9/Mar/2020)

Quandl

Quandl has been around since 2013 and now exists as a part of Nasdaq.

Their mission is broader than just collecting the stock market data, and thus they offer data sets in all sorts different fields from a large and wide range of sources. While not all of their data products are free, their financial data API is available for free, with the following limitations:

Quandl free tier (as of 9/Mar/2020)

Interestingly, Quandl also appears to provide native tools written for R, Python and Excel designed to make it easier to download the data.

Alpha Vantage

Alpha Vantage website includes relatively little information about when they were founded, who they are and what the organisation stands for, save for this relatively broad blurb.

About Alpha Vantage (link)

Nonetheless, they do offer a free tier as below, and appears to be relatively widely used.

Alpha Vantage free tier (as of 9/Mar/2020)

WorldTradingData

Their website (link) similarly contains very little information about who they are, but similarly to the others, they offer a free tier and are relatively well known for it.

Detailed Free Tier Comparisons

The layout of information on each site makes product comparisons very difficult, so below is my attempt at doing so:

Data available

Fortunately, each and all of these APIs appear to provide historical and intra-day U.S. stock prices, and forex data. So most of your needs are probably met by any of these services as far as data availability goes.

For cryptocurrency data, IEX, Quandl and Tiingo make them available, whereas Alpha Vantage and WorldTradingData do not.

If you are after API access to additional (non-price) information, IEX also provides API access to fundamentals and news data. Some of Quandl’s data sources are also free.

Free tier data limits

Because of its slight complexity, let’s leave IEX until the end, and look at the others:

Tiingo : 500 unique symbols per month, 500 requests/hour, 20,000 requests/day, 5 GB/mth (source).

: 500 unique symbols per month, 500 requests/hour, 20,000 requests/day, 5 GB/mth (source). Quandl : 300 requests/10 seconds, 2,000 requests/10 minutes and 50,000 requests/day, if authenticated (source). (20 calls per 10 minutes and 50 calls per day if anonymous)

: 300 requests/10 seconds, 2,000 requests/10 minutes and 50,000 requests/day, if authenticated (source). (20 calls per 10 minutes and 50 calls per day if anonymous) Alpha Vantage : 5 requests/minute and 500 requests/day (source).

: 5 requests/minute and 500 requests/day (source). WorldTradingData: 250 requests/day (25 intraday requests/day) (source).

Now, let’s take a look at IEX. They have a free tier limit of 50,000 core ‘messages’ a month. Each type of request will use up different amounts of messages — so the heavier the data, the more messages will be used.

The 50,000 messages are not a very large amount. On average, it is unlikely to be as much data as Tiingo and Quandl (although it depends on usage), so I would recommend using them judiciously.

This calculator will give you an estimate of how many ‘messages’ will be used for each month of using certain data endpoints.

Happily, IEX is the only one that offers a sandbox testing mode which will return ‘dummy’, or randomised data. The sandbox mode can be used to test and refine your code, and to see how many messages you would have used in real, live mode, and personally it is a big positive.

Documentation

Generally, I have found the IEX Cloud documentation to be the most comprehensive out of those that I looked at.

Here is the link to their documentation:

For example, the IEX documentation clearly goes through response attributes to a historical prices request as such:

IEX Documentation — response attributes (link)

IEX documentation includes request examples, parameter lists, response samples and attributes, as well as additional aspects such as versioning, error codes and security explanations.

From my understanding, IEX is by far the largest organisation out of those listed, and it shows here in the comprehensiveness.

That is not to say that the others’ documentation were lacking, more that the IEX documentation was extremely comprehensive.

Tiingo’s documentation is here:

Tiingo Documentation — response attributes (link)

And Quandl’s here:

Quandl Documentation — response attributes (link)

Both of these are still quite detailed, with example requests and parameters, as well as response examples and parameters. Although not perhaps as impressive as the IEX documentation, these were still quite solid.

And lastly, I would put the Alpha Vantage and WorldTradingData documentations in the last tier.

While it’s not missing any information per se, they are clearly not as complete or explanatory as the others.

Depending on your level of experience with programming and with APIs in general, you might benefit more from the more comprehensive documentations of IEX / Tiingo and Quandl.

Conclusions

I attempted to give a brief overview of the top free financial market data APIs here.

All five listed APIs above are pretty amazing data services, especially given that they operate free of cost. As discussed above, common data types such as historical data or intraday data are available from all providers, and which service to choose may be largely down to personal choice.

Speaking of, my personal preference as a hobbyist in the world of finance would be IEX. For an occasional user such as myself, I would prefer the learning curve to be as shallow as possible, and their extensive documentation would be very helpful, as would be their sandbox mode. Although if I was after additional volume of data, Quandl or Tiingo also appear to be great choices here also.

Generally, though, my (non-expert) opinion is that all of these appear to be pretty solid entry points to the world of financial market data analysis, and you might want to choose one that suits you best.