There is no dominant or typical disturbance, but any of the following may be present:
Inappropriate or constricted affect (the individual appears cold and aloof);
Behavior or appearance that is odd, eccentric or peculiar;
Poor rapport with others and a tendency to withdraw socially;
Odd beliefs or magical thinking, influencing behavior and inconsistent with subcultural norms;
Suspiciousness or paranoid ideas;
Obsessive ruminations without inner resistance;
Unusual perceptual experiences including somatosensory (bodily) or other illusions, depersonalization or derealization;
Vague, circumstantial, metaphorical, over-elaborate or stereotyped thinking, manifested by odd speech or in other ways, without gross incoherence;
Occasional transient quasi-psychotic episodes with intense illusions, auditory or other hallucinations and delusion-like ideas, usually occurring without external provocation. The disorder runs a chronic course with fluctuations of intensity. Occasionally it evolves into overt schizophrenia. There is no definite onset and its evolution and course are usually those of a personality disorder. It is more common in individuals related to people with schizophrenia and is believed to be part of the genetic "spectrum" of schizophrenia. Diagnostic guidelines
This diagnostic rubric is not recommended for general use because it is not clearly demarcated either from simple schizophrenia or from schizoid or paranoid personality disorders, or possibly autism spectrum disorders as currently diagnosed. If the term is used, three or four of the typical features listed above should have been present, continuously or episodically, for at least two years. The individual must never have met criteria for schizophrenia itself. A history of schizophrenia in a first-degree relative gives additional weight to the diagnosis but is not a prerequisite.
Diagnosis
Screening
There are various methods of screening for schizotypal personality. The Schizotypal Personality Questionnaire (SPQ) measures nine traits of STPD using a  self-report assessment. The nine traits referenced are Ideas of Reference, Excessive Social Anxiety, Odd Beliefs or Magical Thinking, Unusual Perceptual Experiences, Odd or Eccentric Behavior, No Close Friends, Odd Speech, Constricted Affect, and Suspiciousness. A study found that of the participants who scored in the top 10th percentile of all the SPQ scores, 55% were clinically diagnosed with STPD. A method that measures the risk for developing psychosis through self-reports is the Wisconsin Schizotypy Scale (WSS). The WSS divides schizotypal personality traits into 4 scales for Perceptual Aberration, Magical Ideation, Revised Social Anhedonia, and Physical Anhedonia. A comparison of the SPQ and the WSS suggests that these measures should be cautiously used for screening purposes of STPD. STPD as a Personality Disorder
DSM-5
In the American Psychiatric Associations DSM-5, schizotypal personality disorder is defined as a "pervasive pattern of social and interpersonal deficits marked by acute discomfort with, and reduced capacity for, close relationships as well as by cognitive or perceptual distortions and eccentricities of behavior, beginning by early adulthood and present in a variety of contexts.