Introduction. Negative interpretation bias (IB) - a tendency to interpret ambiguous stimuli negatively- has been shown to be a risk factor for developing psychiatric disorders. Scrambled Sentences Task (SST) is a widely-used experimental paradigm for measuring IB. In SST, participants are shown a series of 'scrambled' words that can be rearranged into either negative or positive grammatically correct sentences. SST is traditionally administered with time limits and cognitive demand (e.g., working memory task) to prevent response bias. However, a small body of research suggests that the magnitude of convergent validity is comparable between conditions with and without cognitive load, though the role of time limit has not been well-researched. Purpose. Our study aims to address this gap by examining psychometric properties (e.g. reliability, validity) of an untimed, self-administered SST without cognitive load administered online. Method. 66 Canadian university students (80.3% Woman, 28.8% White) completed an online SST task (no time limit or cognitive load) and self-report questionnaires of anxiety and depression (Hospital Anxiety and Depression Scale), and affect (Positive and Negative Affect Schedule). Results. In our sample, SST displayed excellent internal consistency reliability (α = 0.90) and convergent validity (r = .540, p < .001 [depression], r = .544, p < .001 [anxiety]). SST also displayed increment validity above and beyond demographic covariables and negative affect by explaining an additional 30% of variance in depression (ΔF(1, 62) = 28.02, p < .001) and an additional 24% in anxiety (ΔF(1, 62) = 25.38, p < .001). The same pattern of results held with secondary measures of anxiety (GAD-7) and depression (PHQ-9). Conclusions. Our findings suggest that IB can be reliably detected without time limit, cognitive control, or experimenter supervision, substantially improving the ease of use for researchers and participants. Practical applications of this work will be discussed.