UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Date of report (Date of earliest event reported): January 12, 2015

DEMANDWARE, INC.

(Exact Name of Registrant as Specified in Charter)

Registrant’s telephone number, including area code: (888) 553-9216

Not Applicable

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

On January 12, 2015, pursuant to the Agreement and Plan of Merger, dated as of January 9, 2015 (the “Agreement”), by and among Demandware, Inc., a Delaware corporation (the “Company”), Augusta AC Corp., a Delaware corporation and a direct wholly-owned subsidiary of the Company (“Merger Sub”), Tomax Corporation, a Delaware corporation (“Tomax”), and a representative of the selling equityholders of Tomax, the Company completed its acquisition of Tomax, whereby Merger Sub merged with and into Tomax with Tomax continuing as the surviving corporation (the “Merger”), and, as a result of which Tomax has become a wholly-owned subsidiary of the Company.

Pursuant to the Agreement, the Company acquired all of the outstanding capital stock and vested stock options of Tomax for approximately $60 million in cash, subject to certain adjustments and transaction-related payments (the “Cash Consideration”). The Agreement provides for the payment to the Tomax equityholders of up to an additional $15 million in cash and/or in shares of Company common stock upon the achievement of certain milestones relating to the continued post-closing employment of certain key employees of Tomax. A portion of the Cash Consideration will be held in escrow to secure certain indemnification and other obligations of the sellers.

Each of the Company and Tomax has agreed to customary representations, warranties and covenants in the Agreement. The representations and warranties survive for a period of 24 months after the Merger, subject to specified exceptions. The Agreement also includes indemnification obligations in favor of the Company from the sellers, including for breaches of representations, warranties, covenants and agreements made by Tomax in the Agreement.

The foregoing description of the transactions contemplated by the Agreement does not purport to be complete and is qualified in its entirety by reference to the full text of the Agreement, a copy of which was filed as Exhibit 2.1 to the Company’s Current Report on Form 8-K filed on January 12, 2015.

Financial statements of the business acquired will be filed by amendment to this Current Report on Form 8-K (this “Report”) no later than 71 days following the date that this Report is required to be filed.

Pro forma financial information will be filed by amendment to this Report no later than 71 days following the date that this Report is required to be filed.

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

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