Yahoo! Finance‘s public REST APIs and Google Finance‘s public REST APIs are widely used for obtaining financial market data in both open-source projects (e.g. Python’s matplotlib) and commercial software (e.g. Mathworks’ Datafeed Toolbox for Matlab).
This article outlines when such an application is legal (any personal, non-server, use in the spirit of the expected usage of the services) and appropriate (the quality of the data is not suitable for making robust decisions but may be just fine for getting a quick overview of the markets).
From the legal point of view, the areas of concern may be:
- Terms of Service
2.1 Legal Concern – Copyright
There cannot be any copyright claim as market data is not subject to copyrights.
2.2 Legal Concern – Terms of Service
- Spearian offers access to Yahoo! or Google data free-of-charge in the time-unlimited trial version. The price of the product is substantiated by the use of paid-in data, like Open Exchange Rates, and commercial libraries and tools
- Spearian is designed for personal use and doesn’t store or process any Yahoo! or Google data on any of its servers (so no redistribution of data takes place)
- Spearian for Excel, or any program using Yahoo! Finance or Google Finance public and publicly well-documented API, is doing exactly what a web browser is doing and what a user of such an API is expected to do: to open a webpage, enter the address, copy the source of the page or the contents of the page to Notepad, and then parse it for the values of interest and then to copy to Excel or any other target application. In other words, Spearian is a web-browser automation tool, like thousands of other tools, such as Auto-It. One cannot forbid fire (a tool) because it destroys one tree. In fact, the market data retrieval functionality is a template for the Spearian’s WebRead and WebReadIE functions. Furthermore, Spearian is using the Yahoo! or Google services fairly, there is no concern of ripping of the data, like with DVD Rippers
- Even if all above was false which it isn’t, Yahoo! and Google failed to take reasonable steps to prevent this use of data – they could, for example, replace the data with pictures or randomly change the structure of the results or shut the entire REST service down altogether
- Even if all above was false which it isn’t, Yahoo! or Google doesn’t suffer any financial damage. Quite the opposite. Spearian and other similar tools provide Yahoo! and Google free advertisement.
2.3 Legal Concern – Trespassing
However, this doesn’t apply in this case because the amount of downloaded data is minuscule and the download of the financial data is in the spirit and form of the expected usage of the Yahoo! or Google services.
In general, you get what you pay for.
Although Yahoo! and Google Data is free of charge for personal use, its data quality is sometimes lamentable.
As a result, Spearian for Excel is moving more and more in the direction of paid-in data with the key advantage of the paid-in service being the immediate rectification of bad data upon escalation. In addition, the paid-in data sources offer wider variety of data than Yahoo! or Google, such as 1-minute historical price bins or further reference data at very reasonable prices – for example, BarCharts offer for less than 70 USD per user per month unlimited historical global coverage and limited streaming live data.