What is the ACS file format?
Files with the .acs extension are animated character files used by the Microsoft Agent technology. The content of an .acs file is a complete animated character - sprite animation frames, speech balloon settings, and optionally embedded audio - packaged in a single binary container.
Users can interact with these characters, as the technology supports both speech recognition and text-to-speech conversion. .acs files store graphic data - RLE-compressed 8-bit bitmap frames - from which the runtime creates smooth animations.
Animated characters stored in .acs files were used in both applications and on websites. They most commonly served as virtual guides, leading users through installation or form-filling. Characters could also be deployed as interactive consultants or advisors. Well-known examples include Clippit, Merlin, Peedy, and Genie from Microsoft Office 97-2003. For web delivery, characters were split into .ACF (definition) and .aca (animation clips) files.
Microsoft Agent was deprecated in Windows 7 and removed in Windows 8 and later. .acs files cannot run on modern Windows without legacy compatibility shims.
Security & safety
RISK: LOWACS files are passive character data (bitmaps + metadata); they do not contain executable code. The risk is indirect: installing the legacy Microsoft Agent runtime on modern Windows may introduce unmaintained system components. The runtime itself has known security issues (EOL software, no patches since ~2009). Only install on isolated or virtual legacy machines.
Format details
in a nutshell- ArcSDE Connection File (ESRI) - ArcGIS/ArcSDE uses .acs for geodatabase server connection configuration files (XML-based).
- ACT! Contact Sync Settings - Some versions of ACT! CRM software use .acs for synchronisation profile settings.
Programs that open ACS files
Windows2 apps
Microsoft Agent Character Editor
Free Open and edit ACS character files graphically; requires the Agent runtime installed. Legacy tool, runs on Windows XP/7 32-bit only. 
Microsoft Agent Runtime
Free Install the legacy Microsoft Agent 2.0 runtime on Windows XP/Vista/7 (32-bit), then double-click the ACS file or reference it from an application using the Agent ActiveX control. Technical details
deep spec| Format type | Proprietary binary animated character package |
| Container | Microsoft Structured Storage (Compound Document / OLE2) |
| Encoding | Binary, little-endian |
| Magic bytes | `0xABCDABC3` at offset 0 (Version 2 signature); `0xABCDABC4` for `.acf` split-delivery variant |
| Sprite compression | RLE (run-length encoding) applied per animation frame |
| Audio encoding | Embedded PCM or compressed WAV for text-to-speech and character sound effects |
| Color depth | 8-bit indexed (256-color palette) per sprite frame |
| Sprite frame dimensions | Typically 64×64 to 128×128 pixels per frame |
| Typical file size | 200 KB - 5 MB (varies with number of animations and sprite resolution) |
| Speech support | Text-to-speech output and speech recognition input via Microsoft Agent runtime |
| Split-delivery formats | `.acf` (character core for HTTP streaming) + `.aca` (individual animation clips) |
| Windows compatibility | Windows 95 through Windows 7 (deprecated in 7); removed in Windows 8 and later |
| Notable characters | Clippit (Clippy), Merlin, Peedy, Genie - bundled with Microsoft Office 97-2003 |
| Developer | Microsoft Corporation (Microsoft Agent SDK) |
| Released | 1997 (Microsoft Agent 1.5, Windows 95/NT4) |
| Latest version | Version 2 (Microsoft Agent 2.0, 1998) |
| Specification | uploads.s.zeid.me |
ACS conversions
Community Q&A
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