Watch the daily posting of the Fed funds effective rate

Yellen will be conducting a grand policy experiment by hiking interest rates with $2.5 trillion in cash parked in bank funds at the Fed.

For more on the difficulty of hiking, make sure to read:

Those explain the difficulty of raising rates with so much cash chasing yield. The next question is this: How will we know if the Fed was able to hike rates?

That will be answered incrementally in daily doses when the New York Fed announces the previous day's effective Fed funds rate.

When is the effective Fed funds rate published?

It's released daily for the prior day at 5:30 am ET (0930 GMT). The effective rate is the volume-weighted average of rates on trades arranged by major brokers. They also publish the lows and highs.

A great spot to get it quickly is their RSS feed.

The other numbers to watch will be announcements of reverse repos. That's the tool the Fed hopes to use to keep rates above the 0.25% if they hike. if the fed is continually ramping up the program, it's a sign they're struggling.