Drop a UV-vis spectrum saved as JCAMP-DX, Thermo Galactic or Shimadzu SPC, PerkinElmer SP, a Cary CSV export or two columns of text. Each file is read in your browser and drawn over the others on one wavelength axis, in nanometres.
Read the spectra as absorbance or as transmittance. Every λmax of the selected spectrum is picked as a maximum of absorbance; add one or take one away by hand, then save the spectra as JCAMP-DX or the chart as a figure that opens here again.
Drop JCAMP-DX, SPC, PerkinElmer SP, Cary CSV or two-column text files, overlay them, and read off every λmax. The tool needs JavaScript, because every spectrum is read in your browser.