Not a good one that is targeted at non-professional investors. I agree, it's a good opportunity. The issue is that companies have a lot of latitude in how they use XBRL once you get outside of the totally standard financial metrics like revenue, gross profit, total liabilities, etc. And those are the metrics that are already largely available in services such as Yahoo Finance for free. What would be really valuable is taking company specific metrics such as unit volumes, orders, backlog, etc. And that requires a ton of work for each company and some knowledge of what the business does. Also, a lot of that data is not yet broken out into XBRL. For example, look how much data from THO (an RV manufacturer) is useful but not detailed in XBRL fields:

https://www.sec.gov/ix?doc=/Archives/edgar/data/730263/00007...

You can see which parts have XBRL tags by the red lines above and below. If you search the document for "orders" or "units" you can see lots of great information that is basically stranded. I've always thought that it shouldn't be that hard to use a bunch of heuristic rules to find data that is present in the last N 10-K or 10-Q filings (particularly because they tend to reference the previous year results, so you can search for numbers that are the same that are located within K words of certain strings).

But it's hard to do something really useful as a one-person effort with some clever coding, which is probably why the services that are out there are niche and expensive.

I've looked into the XBRL data - it's closer to an XML version of each company's 10-K rather than a unified accounting/reporting system for all public companies. If one company reports their income statement using 20 lines and another uses 15 lines, the XBRL data will show both exactly as they appear in the 10-K and they would not be comparable (unless your software can understand that "Net Interest Expense/(Income)" for one is the same thing as the sum of "Interest Expense" and "Interest Income" for the other). To add to that I've found some companies are filing XBRL is a non-conforming XML standard (probably software issues) and some companies just include the last 3 years of data in every XBRL document (rather than just picking the same data that's reported in the 10-K), making the consumer figure out what is the actual new information in the document.

We use XBRL data for lots of our underlying data on https://docoh.com e.g. financial statements at https://docoh.com/company/1326801/FB/financials and data charting at https://docoh.com/company/data-explorer/1326801

It's not perfect – XBRL is complicated and companies file with lots of proprietary metrics that aren't included in GAAP/FASB standards – but we hope to do more with it in the coming months.

We (https://tagnifi.com) offer standardized fundamentals based on the XBRL data. As others have stated, XBRL is complex and full of corner cases. Our standardization process softens these sharp edges.