The paper presents a novel approach to time-resolved atomic inner-shell spectroscopy using a laser-based sampling system. This system, consisting of a few-femtosecond visible light pulse and a synchronized sub-femtosecond soft X-ray pulse, allows for direct observation of the relaxation dynamics of core-excited atoms in the time domain with attosecond resolution. The authors measured the lifetime of M-shell vacancies in krypton, finding a value of 7.9 ± 1.0 fs. The technique is based on the creation of a core hole by exciting an electron from an inner shell and the subsequent decay of this hole, which is probed using a delayed visible light pulse. The study demonstrates the feasibility of attosecond atomic spectroscopy and opens new avenues for understanding the dynamics of multi-electron systems in strong fields.The paper presents a novel approach to time-resolved atomic inner-shell spectroscopy using a laser-based sampling system. This system, consisting of a few-femtosecond visible light pulse and a synchronized sub-femtosecond soft X-ray pulse, allows for direct observation of the relaxation dynamics of core-excited atoms in the time domain with attosecond resolution. The authors measured the lifetime of M-shell vacancies in krypton, finding a value of 7.9 ± 1.0 fs. The technique is based on the creation of a core hole by exciting an electron from an inner shell and the subsequent decay of this hole, which is probed using a delayed visible light pulse. The study demonstrates the feasibility of attosecond atomic spectroscopy and opens new avenues for understanding the dynamics of multi-electron systems in strong fields.