The paper explores the relationship between expert manual annotation of German spontaneous speech and annotator’s individuality with regard to personality traits, working memory capacity and processing speed. The research question is whether there is a relationship between the annotated sentence length and individual traits of the annotator. The participants were asked to detect sentence boundaries in the transcripts of German spontaneous monologues and to perform several test tasks. Personality traits were examined using the Five Factor Personality Inventory. Working memory capacity was measured through reading span and operation span tasks. To compute processing speed we used Letter Comparison and Pattern Comparison tasks. Linear mixed modelling revealed the significant effect of the personality trait “Neuroticism” on the length of annotated sentences. Contrary to the initial hypothesis, working memory capacity of annotators was not related to sentence length. Processing speed did not have any effect on sentence length either.