Maverick Capital SC 13G/A Castlight Health, Inc.

Exhibit A

Joint Filing Agreement

The undersigned hereby agree that the statement on Schedule 13G/A with respect to the Class B Common Stock, $0.0001 par value per share of Castlight Health, Inc., dated as of February 17, 2015, is, and any amendments thereto (including amendments on Schedule 13D) signed by each of the undersigned shall be, filed on behalf of each of us pursuant to and in accordance with the provisions of Rule 13d-1(k) under the Securities Exchange Act of 1934.

Date:February 17, 2015

MAVERICK CAPITAL, LTD.
By:	Maverick Capital Management, LLC
	Its General Partner
	By:	Lee S. Ainslie III, Manager
		By:	/s/ John T. McCafferty
			John T. McCafferty
			Under Power of Attorney dated
			February 13, 2003

MAVERICK CAPITAL MANAGEMENT, LLC
By:	Lee S. Ainslie III, Manager
	By:	/s/ John T. McCafferty
		John T. McCafferty
		Under Power of Attorney dated
		February 13, 2003

LEE S. AINSLIE III
By:	/s/ John T. McCafferty
	John T. McCafferty
	Under Power of Attorney dated
	February 13, 2003

ANDREW H. WARFORD
By:	/s/ John T. McCafferty
	John T. McCafferty
	Under Power of Attorney dated
	February 11, 2015