In laser-matter interaction experiments it is of paramount importance to be able tocharacterise the laser pulse on target (in-situ) and at full power. This allows pulse optimisationand meaningful comparison with theory, and can shed fundamental new light on pulse distortionsoccurring in or on the target. Here we introduce and demonstrate a new technique based ondispersion scan using the concurrent third harmonic emission from the target that permits the full(amplitude and phase), in-situ, in-parallel characterisation of ultrashort laser pulses in a gas orsolid target over a very wide intensity range that encompasses the1013−1015W cm−2regime ofhigh harmonic generation and other important strong field phenomena, with possible extensionto relativistic intensities also presently inaccessible to other diagnostics.