Predicts the secondary structure a sequence folds into: which bases pair, what loops form and how much free energy the fold releases. Paste one sequence to see how it folds on itself — the hairpin that swallows a primer's 3′ end, the loop a LAMP primer has to open, the fold of an sgRNA. Paste two to see them interact.
The energy model is the complete Turner nearest-neighbour set, including the measured 1×1, 2×1 and 2×2 interior-loop tables and the tri-, tetra- and hexaloop bonuses, rescaled by enthalpy to the temperature you choose. Everything is computed in your browser.
Folding time grows with the cube of the length: a 300-base sequence takes about a second, 1000 bases roughly half a minute. The calculation runs in a background thread, so the page stays usable while it works.
Click a structure to draw it.
Related: PrimerAnalyser reports self-dimers for a single oligo, PrimersList screens a whole set for cross-dimers.