InspectMesh

STL Tools for Inspection, Measurement and Repair

Choose the question you need to answer about an STL file: what it contains, which findings need attention, how large it is, or whether a deliberate change is needed. Use a viewer or checker before changing geometry, and keep the original when exporting a revised copy.

Choose an STL tool by your next decision

Visitor’s question	Next action
What is in this file?	Open the STL viewer
Where should I start before slicing?	Run local STL preflight
Which supported mesh findings exist?	Check STL mesh quality
Reported open boundary: inspect the surface first. Closed material walls can surround an intended passage; do not automatically cap every visible opening.	Interpret STL mesh findings; interpret closure and check the boundary.
Unexpected size: STL declares neither millimetres nor inches. Establish a known physical dimension before changing coordinates.	Check STL dimensions and units; resolve the unit assumption before scaling.
Separate pieces may be unwanted fragments or intended assembly parts. Review what each represents before removal.	Review STL repair options; interpret disconnected shells.
Large file: binary encoding can save bytes without intentionally removing triangles. Triangle reduction changes the represented surface and needs a separate comparison.	Compare STL reduction options after choosing the reduction method.

STL does not declare a physical unit. Establish a known dimension before interpreting size, volume or fit. Processing varies by action: local viewing and preflight are different from explicitly submitting a file for server analysis. Each tool identifies that boundary beside its controls.

After editing, compare the saved STL with the original to review sampled surface changes.

STL tools

Free STL Viewer

Open an STL locally in your browser, inspect it in 3D and see its dimensions and triangle count.

Open STL Viewer

STL Quality Checker

Find common mesh problems before printing, including open edges, non-manifold geometry, duplicate triangles and orientation issues.

Check STL quality

STL Print Preflight Checker

Run mesh, size, printer-fit, sampled wall-thickness and volume checks together before slicing.

Run STL preflight

STL Repair Tool

Review and remove disconnected pieces in your browser, or run conservative server cleanup for duplicate and degenerate triangles and simple orientation issues.

Review STL pieces or clean

STL Watertight Checker

Check whether an STL has a closed surface, open edges or possible holes.

Check watertightness

STL Manifold Checker

Count exposed and over-shared STL edges plus vertex-connected groups; review the surface before repair.

Check STL topology

STL Dimensions Checker

Measure STL bounds under an explicit unit assumption, propose a proportional scale and compare nominal printer fit.

Measure an STL file

STL Scale Tool

Resize an STL proportionally by percentage, target dimension, or an assumed unit conversion, then download it locally.

Scale an STL

STL Wall Thickness Checker

Estimate sampled wall thickness locally and identify areas that may need closer print-preparation review.

Check wall thickness

STL Overhang Checker

Screen wound STL triangles by build direction and a strict angle-from-vertical threshold, with explicit assumed area units.

Check overhang risk

STL Splitter

Make a supported planar cut, export separate copies and review the resulting surfaces before slicing.

Split an STL

STL Volume Calculator

Interpret supported STL enclosed volume under an explicit unit assumption and calculate optional solid mass.

Calculate STL volume

STL Triangle Counter

Count triangles and understand mesh complexity before slicing or sharing.

Count STL triangles

STL File Size Reducer

Convert ASCII STL to binary locally or simplify a copy with clear before-and-after file and triangle counts.

Reduce STL file size

STL to 3MF Converter

Convert an STL into a basic 3MF locally and choose the unit for its existing coordinates.

Convert STL to 3MF

Choosing how to place a model before slicing? Use the 3D Print Orientation Planner.

Browse all 3D file tools

Choose a path by task

Starting with an unfamiliar file? Run STL Print Preflight, then follow the finding to a focused check.
Suspect an open surface? Use the STL Watertight Checker and inspect the hole before capping it.
Found detached pieces? In STL Repair, all pieces start kept. Keep largest part proposes a reversible surface-area selection; review it before downloading. First identify intended shells before removing any.
Need an intentional cut between parts? Use the STL Splitter for a supported planar cut, then verify both exported meshes. Use the split diagnosis guide when the input, plane, contour or processing stage is rejected, or the alignment-pin guide when planning the separate assembly. An intentional cut is a different task from removing detached fragments.
File too large? The local reducer compares binary re-encoding with lossy triangle reduction; read the size-reduction decision guide before choosing a target.
Concerned about non-manifold edges or disconnected shells? Run the STL Manifold Checker; it checks different topology findings from the open-edge check.
Want to rotate and inspect the model before deciding what to do? Open the Free STL Viewer.
Need the model's overall size or printer-fit dimensions? Use the STL Dimensions Checker; confirm the unit assumption before interpreting measurements.
Need to change size without changing proportions? Use the STL Scale Tool and verify the resulting dimensions.
Checking whether thin regions may need attention? The STL Wall Thickness Checker provides an approximate sampled preflight, not a guarantee of printable walls.
Need a quick measure of mesh complexity? The STL Triangle Counter reports the triangle count; it does not reduce the file.
Estimating solid-model volume or material mass? Use the STL Volume Calculator; the estimate depends on a valid closed volume and selected material density.
Need a basic 3MF with an explicit unit for the STL coordinates? Use the STL to 3MF Converter.

Choose a size task

Establish the coordinate unit, calculate a final percentage, then resize and reopen a separate copy. For feature questions, choose the appropriate measurement.

For build metadata and geometry conversion, choose a 3MF build check.