The free-verse poem "Song of Myself" by Walt Whitman is considered one of the greatest works of American literature. It was first published in 1855 as part of Whitman's collection Leaves of Grass. The first edition of the poem had no sections. These were added later, as was the title.
As for your question about the tone of the poem, there is no one answer. After you read it carefully, you may find the answer to this question to be different than someone else's who reads it. As Whitman says in the poem:
You are also asking me questions and I hear you,
I answer that I cannot answer, you must find out for yourself.
To help you find your own personal answer, I will suggest some possible answers, and then you can choose which interpretation seems best from your own perspective.
The tone of the poem is exuberant. Whitman embraces and is in love with all existence. He revels in life and in all that he observes of life. The tone is accepting. Whitman regards all people—men and women, the rich and the poor, free people and slaves, the young and the old, people from all occupations and walks of life—with acceptance. In this respect, we can also say that the tone is universal in its total acceptance of every facet of existence. The tone is also immediate. The poet looks not to the past or to the future but lives in the present.
The tone is passionate, and in parts of the poem it is even overtly sexual. Whitman writes of the ecstasy of the touch of flesh to flesh and makes no secret of the fact that he has had multiple lovers. The tone is also spiritual. Whitman mentions God numerous times and emphasizes that God is present in all the great things and in the minutia of life.
Additionally, the tone is empathetic. To be empathetic means that you understand and are sensitive to the thoughts and feelings of others. Related to this is Whitman's embrace of the diversity in people. The poem includes long lists of descriptions of many different types of people, and Whitman makes it clear that he accepts and embraces them all.
In conclusion, this wonderful poem includes all of these tones, so after you read it for yourself, decide which of them are most important to you personally (or even one that isn't mentioned).