Structure validation in chemical crystallography is a critical process that ensures the accuracy and reliability of crystal structure reports. Introduced about 12 years ago, automated structure validation has evolved into a web-based IUCr service, checkCIF/PLATON, which checks the completeness, quality, and consistency of crystal structure data. The validation process generates a list of ALERTS highlighting issues that need correction, checking, or comment. This has largely eliminated obvious problems in published structure reports, such as incorrect space group assignments. The validation process addresses three key questions: completeness of the reported information, quality of the analysis, and correctness of the structure. Structures are classified into four quality classes based on their data quality and analysis. Class I structures are high-quality, while Class IV structures are incorrect and can have serious implications for research. Validation is particularly important for addressing Class IV structures, as they can lead to incorrect conclusions. The current IUCr validation tool, checkCIF/PLATON, is still far from the ideal tool that would unambiguously assign one of the four quality classes to a structure. Instead, it produces a list of ALERTS classified by severity. These alerts are addressed by the investigator and evaluated by experts. The validation criteria are often empirical and based on experience rather than scientific principles. Validation of diffraction data is crucial for ensuring the accuracy of crystal structure reports. The availability of reflection data allows for detailed analysis of issues such as symmetry and enantiopurity. However, referees of chemical journals often lack access to this data, leading to potential errors in publication. Examples of erroneous structures include those with missed symmetry, incorrect H atom positions, and misassigned atom types. These errors can have significant impacts on the interpretation of chemical structures. Validation tools like PLATON/VALIDATION and checkCIF/PLATON are used to detect and correct these issues. The validation process is essential for ensuring the quality of crystal structure reports. It helps identify and correct errors that might otherwise go unnoticed, ensuring that published structures are accurate and reliable. Despite advancements, challenges remain in validating structures, particularly in cases involving charge balance and twinning. Ongoing improvements and extensions to validation tools are necessary to address these issues and ensure the reliability of crystallographic data.Structure validation in chemical crystallography is a critical process that ensures the accuracy and reliability of crystal structure reports. Introduced about 12 years ago, automated structure validation has evolved into a web-based IUCr service, checkCIF/PLATON, which checks the completeness, quality, and consistency of crystal structure data. The validation process generates a list of ALERTS highlighting issues that need correction, checking, or comment. This has largely eliminated obvious problems in published structure reports, such as incorrect space group assignments. The validation process addresses three key questions: completeness of the reported information, quality of the analysis, and correctness of the structure. Structures are classified into four quality classes based on their data quality and analysis. Class I structures are high-quality, while Class IV structures are incorrect and can have serious implications for research. Validation is particularly important for addressing Class IV structures, as they can lead to incorrect conclusions. The current IUCr validation tool, checkCIF/PLATON, is still far from the ideal tool that would unambiguously assign one of the four quality classes to a structure. Instead, it produces a list of ALERTS classified by severity. These alerts are addressed by the investigator and evaluated by experts. The validation criteria are often empirical and based on experience rather than scientific principles. Validation of diffraction data is crucial for ensuring the accuracy of crystal structure reports. The availability of reflection data allows for detailed analysis of issues such as symmetry and enantiopurity. However, referees of chemical journals often lack access to this data, leading to potential errors in publication. Examples of erroneous structures include those with missed symmetry, incorrect H atom positions, and misassigned atom types. These errors can have significant impacts on the interpretation of chemical structures. Validation tools like PLATON/VALIDATION and checkCIF/PLATON are used to detect and correct these issues. The validation process is essential for ensuring the quality of crystal structure reports. It helps identify and correct errors that might otherwise go unnoticed, ensuring that published structures are accurate and reliable. Despite advancements, challenges remain in validating structures, particularly in cases involving charge balance and twinning. Ongoing improvements and extensions to validation tools are necessary to address these issues and ensure the reliability of crystallographic data.