Poetic devices are the same as literary devices plus the addition of some structural features that are specific to poetry. Some structural features follow: "On the Grasshopper and the Cricket" is a fourteen line sonnet with a rhyme scheme of a b b a a b b a c d e c d e with no end couplet making it a Petrarchan sonnet instead of a Shakespearean sonnet.
The rhythm is in iambs ( ^ / ) for five feet of repeating patterns: it is in iambic pentameter. The sonnet structure is an octave of eight non-alternating lines and six ending lines comprising a sestet. There are voltas (turns in topic) at lines 5 and 9 where the topics turn from the general voice of the poetry of nature to the specific voice of the grasshopper (5) and the from the grasshopper to a comparison of the cricket in winter to the grasshopper of summer.
Some poetic devices classed as techniques used by Keats follow: The poem is based upon a double metaphor in which the poetry of earth is compare to the grasshopper and the cricket is compared to the grasshopper. Keats also employs personification (e.g., "he rests at ease," "frost has wrought") and sensory imagery (e.g., "voice will run from hedge to hedge").
Keats also uses the figures of speech that are word schemes, which manipulate sounds, letters, syntax and words to create rhetorical effects. He uses anastrophe, a type of hyperbaton, that places the adjective on the wrong side of the noun (e.g., "ceasing never," "warmth increasing ever"). He also uses the type of hyperbaton called apocope in which the word-final letters or syllables are dropped for effect or to fit a meter. An example is "lone winter evening" in which the -ly is dropped from lonely to create lone.