STLRepair is an online tool for checking and repairing STL mesh files used in 3D printing. Its primary function is to detect common geometric errors, including open boundaries, non-manifold edges, duplicate triangles, and zero-area faces. The tool offers free basic repair that runs locally in the user’s browser. An optional cloud-based advanced repair service is available for more complex models and is provided on a paid basis. Users can upload STL files in binary or ASCII format without requiring an account for basic repair. The workflow consists of uploading a file, previewing the model, reviewing a mesh report, applying free base-level fixes or selecting advanced repair, inspecting the changes and remaining warnings, and then downloading the repaired STL. The tool can accept up to five files at once and processes each file individually. Free basic repair is subject to local device memory limits and a file size cap of 25 MiB or 250,000 triangles. Advanced repair options include a one-time purchase for up to 50 MiB per file and a Pro subscription that supports up to 100 MB per file. The software is designed for users who encounter mesh errors in slicer warnings, from AI-generated STL exports, or from 3D scans and downloaded models. The free repair handles supported cleanup tasks such as removing degenerate faces, while advanced repair attempts additional methods for eligible complex meshes. The repaired file is checked again before delivery, but the tool does not certify printability because it does not evaluate self-intersections or wall thickness. An advanced repair purchase is charged only for accepted results; unsuccessful repairs do not consume the purchase.