Is my IFC file uploaded anywhere?

No. Files are parsed entirely in your browser via web-ifc, a WebAssembly build of the open-source IFC parser. Nothing leaves your machine. The app works completely offline once loaded.

Can I use it with confidential models under NDA?

Yes. Because all processing happens in your browser and no data is ever transmitted to any server, you can safely use it with confidential project models under NDA. There is no service agreement to review with your client — no data changes hands.

Can I share the validation results with my team or client?

Yes. After running validation, click Share Report to copy a link that encodes the full Health Score and issue list directly in the URL — no file upload, no server, no account required. You can also export results as JSON, CSV, or a Validation Certificate. The IFC file itself never leaves your browser.

Yes, fully. IFC Viewer Online works on any modern browser — Chrome, Edge, Firefox, and Safari on both Mac and Windows. No plugin, no installation, no operating system restriction.

What happens if my IFC file is very large?

The app handles files up to 2 GB. Performance depends on your device — files under 200 MB load well on most modern hardware. Once parsed, geometry is cached in OPFS so every subsequent load of the same file is instant, even offline.

How does the validation work?

The validator runs 44 built-in rules in a background Web Worker so the UI stays responsive. Rules cover GUID duplicates, spatial hierarchy, orphan elements, naming conventions, missing type assignments, ISO 19650 property sets, LOD completeness, clash detection, proxy overuse, coordinate offset, storey-elevation integrity, unit consistency, and more. You can also run a buildingSMART IDS specification against the model. Every model receives a Health Score from 0 to 100. Results stream in as each rule completes.

Can I fix errors and re-export a corrected IFC?

Yes. All edits (GUID fixes, renames, property value changes) are held as non-destructive diffs with full undo/redo. Clicking Export IFC applies all diffs to the original binary in a Web Worker and downloads the corrected file — no server involved.

What IFC versions are supported?

IFC2x3, IFC4, IFC4x1, and IFC4x3. The viewer uses the open-source web-ifc parser — the same engine used by most modern BIM tools and @thatopen/components. Outdated schemas are automatically flagged by the validator.

What measurement tools are available?

You can measure lengths between any two points, areas of surfaces, volumes of enclosed elements, and individual edge lengths — all directly in the 3D viewport. Measurements persist as labelled annotations and can be exported alongside your model.

Can I load multiple IFC files at once?

Yes. Load as many IFC files as your device memory allows. Each model has independent visibility, transforms, validation, quantity takeoff, and export. Use the Scene panel to manage, reorder, or remove models at any time.

Does it work offline?

Yes, once the page is loaded. The WebAssembly parser and WebGL renderer run entirely in the browser. Parsed geometry is cached in OPFS so repeat loads are instant even without a network connection.

What are the file size limits?

There is no enforced limit — performance depends on your device. Files up to ~200 MB typically load well on modern hardware. The OPFS geometry cache means you only pay the parse cost once per file.

Is it free? Can I use it for commercial projects?

Yes, completely free. The source code is MIT-licensed. You can use the live app or fork the repository for your own projects, including commercial ones.

Back to the BIM & IFC blog

Validation · 2026-05-20 · 8 min

Duplicate GUIDs in IFC: The Silent Error That Breaks Everything

Three weeks into a BCF coordination issue, you realise the comments reference elements that have vanished from the model. The model looks fine. The error: two elements sharing the same GlobalId — and every tool downstream has been silently confused since day one.

Duplicate GUIDs in IFC: The Silent Error That Breaks Everything — IFC Viewer Online article cover

What Is a GlobalId in IFC?

Every entity in an IFC file that inherits from IfcRoot — which includes every physical element, space, storey, building, and site — has a GlobalId attribute. It's a 22-character string using a custom base-64 alphabet, and it's supposed to be globally unique, stable across revisions, and persistent across software round-trips.

#100 = IFCWALL('3LYa_FRDj3zhLfyYoQv6Jr', $, 'Exterior Wall - 300mm', $, $, #88, #92, $, .NOTDEFINED.);
#101 = IFCDOOR('3LYa_FRDj3zhLfyYoQv6Jr', $, 'Door D001', $, $, #89, #93, $, .NOTDEFINED.);

// Both elements share the same GlobalId — IFC schema violation.

The IFC spec (ISO 10303-21) forbids duplicate GlobalIds. But the spec can't enforce it — file parsers load whatever they're given. Most parsers don't even check. The result: a structurally valid file that two elements claim as their own.

Why Duplicates Happen

Revit re-exports: By default, some Revit export configurations regenerate GUIDs on every export. Two exports of the same model produce different GUIDs — then if a third export copies an element from an older file, you get collisions.
Copy-paste in authoring tools: Duplicating a family instance without triggering a GUID refresh — common in ArchiCAD and Vectorworks — produces two elements with identical GlobalIds.
Model merges: Merging two IFC files without checking for GUID collisions between them is a guaranteed way to introduce duplicates, especially if both files were exported from the same source model.
Script-generated GUIDs: Custom export scripts that generate GUIDs using plain UUID (32 hex chars) and truncate to 22 characters without the correct base-64 encoding — producing non-unique strings or invalid format.

What Duplicate GUIDs Break

BCF coordination

BCF issues reference elements by GlobalId. A duplicate means comments attach to whichever element the receiving tool happens to load first — the other element becomes unreachable by reference.

Revit IFC links

Revit's IFC link resolver uses GlobalIds to track element versions across model updates. Duplicates cause elements to randomly switch identity between updates, breaking change-tracking.

CDE asset registers

CDEs like ACC and ProjectWise index IFC elements by GlobalId for handover data. Duplicates create phantom assets that appear in the register but can't be located in the model.

COBie exports

COBie sheets key facilities management data to IfcSpace and IfcAsset GlobalIds. Duplicate spaces produce duplicate rows in the FM handover package.

How to Detect Duplicate GUIDs

Run validation before any CDE delivery. The RULE_DUPLICATE_GUID check flags every element that shares a GlobalId with another — and it's auto-fixable, meaning the validator can generate new spec-compliant GUIDs for the duplicates in one click.

Validate the Duplex model live

Open the buildingSMART duplex in the viewer to see what a clean validation report looks like. Then try opening one of your own project files to check for duplicate GUIDs.

IFC2x3 · 2.4 MB

Open the interactive IFC viewer

How to Fix Duplicate GUIDs

Option 1: Auto-fix in the validator

The IFC Viewer validator marks duplicate GUID issues as auto-fixable. Click the fix icon next to any RULE_DUPLICATE_GUID issue and a new spec-compliant GlobalId is generated — a 22-character string using the correct IFC base-64 alphabet (0–9, A–Z, a–z, _, $) with a leading character in 0–3.

Option 2: Fix in Revit

In Revit with the open-source IFC exporter: File → Export → IFC → Modify Setup → Advanced tab → set "Export IFC GUIDs" to "Keep Existing". This preserves the stable GlobalIds Revit internally assigns rather than regenerating them on each export.

Option 3: Fix in ArchiCAD

In ArchiCAD: File → Save As → IFC 2x3 → Settings → IFC Translation Settings → enable "Write stable GlobalIDs (from AC internal IDs)". Without this enabled, ArchiCAD generates new GUIDs on every export.

Duplicate GUIDs in IFC: The Silent Error That Breaks Everything