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STEP File Analyzer and Viewer

STEP File Analyzer and Viewer screenshot

The free STEP File Viewer supports part geometry, dimensions and tolerances, sketch and supplemental geometry, and datum targets that is displayed in a web browser.  See the examples below.

The STEP File Analyzer generates a spreadsheet or CSV files of all entity and attribute information; reports and analyzes any semantic PMI, graphical PMI, and validation properties for conformance to recommended practices; and checks for basic STEP file format errors.

STEP (ISO 10303 –STandard for Exchange of Product model data) files are also known as Part 21 files with a file extension of .stp, .step, or .p21.

STEP files are used to represent part geometry and product and manufacturing information (PMI) that is used for data exchange and interoperability between Computer-Aided Design (CAD), Manufacturing (CAM), Analysis (CAE), and Inspection (CMM) software. STEP files are also used for long-term archiving and retrieval of product data (LOTAR).

STEP File Viewer

STEP files can be opened to view (in an online web browser): part geometry, tessellated part geometry, sketch geometry, graphical PMI for geometric dimensioning and tolerancing (GD&T), supplemental geometry, datum targets, and finite element models.  Nested assemblies are supported where one STEP file contains the assembly structure with external file references to individual assembly components that contain part geometry.  STEP part geometry is converted to X3D for the viewer with the NIST STEP to X3D Translator.

STEP File Analyzer visualization


A spreadsheet simplifies analyzing information from the STEP file at an entity and attribute level. Typical STEP file viewers show a 3D view of the part or model represented by the STEP file. The viewers usually have a high-level hierarchical display of the information in the STEP file where the user can drill down to individual attributes of parts. However, there is no way to analyze all of the actual STEP entities and their attributes at once. The STEP File Analyzer and Viewer provides the analysis capability by creating a spreadsheet from the STEP file.  The analysis reports are defined below.

  • STEP-File-Analyzer-sfa.xlsx - Spreadsheet generated from an AP203 file. Validation Properties are report on the property_definition worksheet. PMI Presentation is reported on the annotation_occurrence worksheet.
  • STEP-File-Analyzer-PMI-Representation-sfa.xlsx - Spreadsheet generated from an AP242 file. Detailed PMI Representation reports (see explanation below) are on various entities indicated on the Summary worksheet. There are also PMI Representation Summary and Coverage Analysis worksheets. The Summary and Coverage Analysis worksheets are color-coded by the number of expected PMI annotations and elements in the NIST CAD models.
  • STEP-File-Analyzer-Coverage.xlsx - Spreadsheet generated when processing Multiple STEP files. The File Summary worksheet shows the distribution of STEP entities across all of the files. The Coverage Analysis worksheet shows coverage of PMI Representation concepts from the STEP file and CAx-IF Recommended Practices.


Reports can be generated for PMI Representation, PMI Presentation, and Validation Properties based on Recommended Practices defined by the CAx Implementor Group.  Examples of the spreadsheet reports are shown above.

PMI (Product and Manufacturing Information) consists of annotations and attributes that define product geometry and product specifications. PMI includes annotations to specify Geometric Dimensioning and Tolerancing (GD&T), as well as non-geometric data such as surface texture specifications, finish requirements, process notes, material specifications, and welding symbols. GD&T is a symbolic language used to communicate tolerances on manufactured parts.

PMI Representation (also known as semantic PMI) includes all information necessary to represent GD&T without any graphical presentation elements. PMI Representation is associated with CAD model geometry and is computer-interpretable to facilitate automated consumption by downstream applications for manufacturing, measurement, inspection, and other processes. The PMI Representation spreadsheet report includes information related to GD&T such as Dimensional Tolerances, Geometric Tolerances, and Datum Features. PMI Representation is typically found in AP242 files.

PMI Presentation (also known as graphical PMI) consists of geometric elements such as lines and arcs preserving the exact appearance (color, shape, positioning) of the GD&T annotations. PMI Presentation is not intended to be computer-interpretable and does not carry any representation information, although it can be linked to its corresponding PMI Representation. The PMI Presentation spreadsheet report includes the type of the PMI and geometry entities such as polylines that make up the PMI Presentation. Associated geometry, PMI Representation, and Saved Views are also reported. 

Validation Properties are quantities related to features of a CAD model that are computed by the native CAD software used to validate the import of those quantities. The Validation Properties spreadsheet report include geometric, PMI, assembly, annotation, attribute, and tessellated validation properties.

Coverage Analysis worksheets for PMI Representation and PMI Presentation are also generated when processing single or multiple STEP Files. Coverage is based on characteristics of PMI defined in the Recommended Practices.  If a STEP AP242 file from a NIST CAD model is processed, then the PMI found in the STEP file is checked against the expected PMI in the corresponding NIST test case.  The coverage analysis worksheets are color-coded by the expected PMI in each test case.

PMI Representation Summary worksheet
PMI Representation Summary worksheet

Syntax Checker

The software includes a syntax checker that checks for basic syntax errors and warnings in the STEP file related to missing or extra attributes, incompatible and unresolved entity references, select value types, illegal and unexpected characters, and other problems with attributes.  Any STEP file errors might help you diagnose errors importing STEP files into CAD software.  There should not be any of these types of errors in a STEP file.  Errors should be fixed to ensure that the STEP file conforms to the STEP schema and can interoperate with other software.  There are other validation rules defined by STEP schemas (where, uniqueness, and global rules, inverses, derived attributes, and aggregates) that are not checked.

Testing STEP Implementations

The CAx Interoperability Forum (CAx-IF) tests software implementations of AP242 and tested AP203 and AP214 in the past.  The CAE Interoperability Forum (CAE-IF) tests software implementations of AP209.  The objective of the CAx-IF is to advance CAx (mainly Computer-Aided Design and Engineering) software system STEP translator development and to ensure that user requirements for interoperability are satisfied.  The CAx-IF and CAE-IF are joint testings effort between PDES, Inc., prostep ivip, and  AFNeT.  prostep and AFNeT have published AP242 benchmark tests.

To test how well your CAD system implements STEP AP242 PMI, download the NIST PMI CAD models, open one of the models, export an AP242 file with PMI, and process it with the STEP File Analyzer and Viewer.  In the resulting spreadsheet, the PMI Representation Summary worksheet will indicate how well the AP242 PMI matches the expected PMI in the NIST PMI CAD model test case definitions.  Differences might be due to how some PMI was modeled in the CAD system or how the PMI was exported to the STEP file.


The STEP File Analyzer and Viewer supports all commonly used STEP file formats, also known as Application Protocols (AP), including those listed below. An AP is the implementable part of ISO 10303 on which translators are based on in a particular engineering domain.

Some other EXPRESS schemas are also supported.


Created December 7, 2012, Updated September 22, 2020