Do any banks offer data feeds of personal accounts via any form of API? I'm essentially looking to check balances on accounts without logging into their website.
I remember reading about a universal banking protocol at some point... and maybe mint.com uses it to access accounts? Does mint.com have a special relationship with each bank, or can I leverage their method?
Edit: For my requirements, I'm only interested in accessing my own financial data.
Look up OFX format on the web. That (I believe) is a generic format for the banking industry.
Also check out: http://stackoverflow.com/questions/2731497/open-source-personal-finance-apis
You could try Swift (see message types), its not the kind of thing you can just set up though, you'd have to speak to each institution you wanted to work with.
There is a standard protocol known as OFX (ofx.net) that might meet your needs. Microsoft Money and Quicken both use it to update data.
API access
You will need to check with each institution if they provide an API for direct access. Some will provide access over a dial-up line, others have more modern IP based service. Each will likely require you to register and pay a fee.
Easier is to require the user to download their statement from the bank and import it into your application. Most online banking systems provide this functionality.
Formats
Either way, there are several formats supported by banks (taken from here).
You might see OFX referred to as Quickbooks, Microsoft Money 2005 or Sage Line 50. QIF is sometimes called Quicken 98 or 2000, or Microsoft Money 2003.
CSV formats will be propriety per institution and require parsing logic developed for each instance.
Who uses what format
The UK banks that support OFX or QIF formats are: