When we think about the tone of a work we are referring to the attitude that a writer takes towards a particular character, situation or the work as a whole. Normally the tone of a work can be expressed through a simple adjective. It is clear that in this poem the sight of the daffodils gives the speaker a real sense of joy and fulfilment as he sees them "fluttering and dancing in the breeze." The way that they are compared to "stars that shine" and personifies them as "dancing." Not only that, but this becomes a cherished memory for the speaker in the future, as the last stanza explains:
For oft, when on my couch I lie
In vacant or in pensive mood,
They flash upon that inward eye
Which is the bliss of solitude;
And then my heart with pleasure fills,
And dances with the daffodils.
Thus we can say that the tone of this poem is joyful and contemplative. This was based on an actual experience of Wordsworth in the Lake District in the UK--a part of the country renowned for its natural beauty. Note the emotional impact of this sight and its memory on Wordsworth. It is something that he keeps on going back to so that he can "dance with the daffodils" but also regain that sense of joy and pleasure.