EXHIBIT 5.01

                                 March 29, 2002

Keynote Systems, Inc.
777 Mariners Island Boulevard
San Mateo, CA 94404

Ladies and Gentlemen:

     At your request, we have examined the registration statement on Form S-8
(the "Registration Statement") filed by you with the Securities and Exchange
Commission (the "Commission") on or about March 29, 2002, in connection with the
registration under the Securities Act of 1933, as amended, of 1,395,169 shares
of your common stock (the "Stock"), subject to issuance upon exercise of stock
options granted or to be granted under your 1999 Equity Incentive Plan (the
"Incentive Plan"), and of 279,034 shares of Stock subject to purchase rights
granted or to be granted under your 1999 Employee Stock Purchase Plan (the
"Purchase Plan" and together with the Incentive Plan, the "Plans").

     In rendering this opinion, we have examined the following:

     (1)  your Amended and Restated Certificate of Incorporation, certified by
          the Delaware Secretary of State on January 12, 2000;

     (2)  your bylaws, certified by your Secretary on February 29, 2000;

     (3)  the Registration Statement, together with the exhibits filed as a part
          thereof or incorporated therein by reference,

     (4)  the registration statement on Form S-8 (File No. 333-73244) filed by
          you with the Commission on November 13, 2001, together with the
          exhibits filed as a part thereof or incorporated therein by reference;

     (5)  the registration statement on Form S-8 (File No. 333-87791) filed by
          you with the Commission on September 24, 1999, together with the
          exhibits filed as a part thereof or incorporated therein by reference,
          including the Incentive Plan and related forms of stock option
          agreement and stock option exercise agreement, and the Purchase Plan
          and related forms of enrollment form, subscription agreement, notice
          of withdrawal and notice of suspension;

     (6)  the prospectuses prepared in connection with the Registration
          Statement;

     (7)  the minutes of meetings and actions by written consent of your
          stockholders and Board of Directors that are contained in your minute
          books and the minute books of your predecessor, Keynote Systems, Inc.,
          a California corporation, that are in our possession;

     (8)  a certificate from your transfer agent of even date herewith verifying
          the number of issued and outstanding shares of your capital stock as
          of March 28, 2002 and a list of options respecting your capital stock
          and of any rights to purchase capital stock that was prepared by you
          and dated March 28, 2002 verifying the number of such issued and
          outstanding securities; and

     (9)  a Management Certificate addressed to us and dated of even date
          herewith executed by you containing certain factual and other
          representations.

     In our examination of documents for purposes of this opinion, we have
assumed, and express no opinion as to, the genuineness of all signatures on
original documents, the authenticity and completeness of all documents submitted
to us as originals, the conformity to originals and completeness of all
documents submitted to us as copies,



the legal capacity of all persons or entities executing the same, the lack of
any undisclosed termination, modification, waiver or amendment to any document
reviewed by us and the due authorization, execution and delivery of all
documents where due authorization, execution and delivery are prerequisites to
the effectiveness thereof. We have also assumed that the certificates
representing the Stock will be, when issued, properly signed by your authorized
officers or their agents.

     As to matters of fact relevant to this opinion, we have relied solely upon
our examination of the documents referred to above and have assumed the current
accuracy and completeness of the information obtained from the documents
referred to above and the representations and warranties made by you to us,
including, but not limited to, those set forth in the Management Certificate. We
have made no independent investigation or other attempt to verify the accuracy
of any of such information or to determine the existence or non-existence of any
other factual matters; however, we are not aware of any facts that would cause
us to believe that the opinion expressed herein is not accurate.

     We are admitted to practice law in the State of California, and we render
this opinion only with respect to, and express no opinion herein concerning the
application or effect of the laws of any jurisdiction other than, the existing
laws of the United States of America, of the State of California and, with
respect to the validity of corporate action and the requirements for the
issuance of stock, of the Delaware General Corporation Law, the Delaware
constitution and reported judicial decisions relating thereto.

     Based upon the foregoing, it is our opinion that the up to 1,674,203 shares
of Stock that may be issued and sold by you upon exercise of (a) stock options
granted or to be granted under the Incentive Plan and (b) purchase rights
granted or to be granted under the Purchase Plan, when issued, sold and
delivered in accordance with the applicable plan and purchase agreements to be
entered into thereunder, and in the manner and for the consideration stated in
the Registration Statement and/or the relevant prospectus, will be validly
issued, fully paid and nonassessable.

     We consent to the use of this opinion as an exhibit to the Registration
Statement and further consent to all references to us, if any, in the
Registration Statement, the prospectuses constituting a part thereof and any
amendments thereto. This opinion is intended solely for use in connection with
the issuance and sale of Stock subject to the Registration Statement and is not
to be relied upon for any other purpose. We assume no obligation to advise you
of any fact, circumstance, event or change in law or the facts that may
hereafter be brought to our attention whether or not such occurrence would
affect or modify the opinions expressed herein.

                                        Very truly yours,

                                        /s/  Fenwick & West LLP

                                        FENWICK & WEST LLP