What is the HML file format?
.hml files are TestList configuration files used by HostMonitor, a Windows network monitoring application developed by KS-Soft. Each file stores the complete set of monitoring tests configured for a HostMonitor installation - including the hosts being watched, the monitoring method for each (Ping, HTTP, HTTPS, SMTP, TCP port, FTP, and dozens of other protocols), alert thresholds, notification settings, and test schedules.
The format is a proprietary text-based structure using section headers and key-value entries. Tests are organized hierarchically into folders, mirroring the folder tree visible in the HostMonitor interface. A single .hml file can describe hundreds or thousands of test entries for large network environments, making file sizes range from a few kilobytes to several megabytes.
.hml files are useful for:
- Backing up an entire monitoring configuration before upgrading or migrating HostMonitor to a new server.
- Sharing or merging test lists between multiple HostMonitor installations.
- Inspecting the configuration in a text editor (manual editing is not recommended due to complex interdependencies between entries).
KS-Soft also ships HML Manager, a standalone companion utility that allows viewing, merging, and exporting .hml files without a live HostMonitor instance running.
HostMonitor is Windows-only commercial software; the .hml format is entirely proprietary to KS-Soft and is not supported by any third-party monitoring platforms.
Security & safety
RISK: LOWHML files are text configuration files for network monitoring software. They may contain IP addresses, hostnames, and credentials (SNMP community strings, HTTP passwords) for monitored devices - treat them as sensitive configuration data. Not a malware vector.
Format details
in a nutshell- HyperMarkup Language file (rare) - Some older tools used .hml as an alias for HTML-like markup; extremely uncommon today.
Programs that open HML files
Windows3 apps
HostMonitor
Paid File → Open TestList → select the .hml file to load the full monitoring configuration.
HML Manager
Free Open HML Manager, then File → Open to browse and view the test list without running HostMonitor.
Notepad / any text editor
Free Open for read-only inspection of host/test entries; editing manually is not recommended. Technical details
deep spec| Format type | Proprietary text-based configuration file with section headers |
| MIME type | application/octet-stream (no registered MIME type) |
| Text encoding | Windows-1252/ANSI (older versions); UTF-8 (modern versions) |
| Encryption | None (plaintext) |
| Typical file size | 10 KB - 5 MB (depends on number of monitored hosts and tests) |
| Structure | Hierarchical folder/test sections; each entry specifies host address, protocol type, thresholds, alert rules, and schedule |
| Supported monitoring protocols | Ping, HTTP, HTTPS, SMTP, TCP port, FTP, DNS, SNMP, and dozens of additional check types |
| Associated operating system | Windows only |
| Developer | KS-Soft (proprietary; no public specification) |
| Import/export support | Supported between HostMonitor installations for backup and migration |
| Companion utility | HML Manager - standalone tool for viewing and merging .hml files without a running HostMonitor instance |
| Manual editing | File is human-readable in a text editor but manual editing is not recommended due to complex entry interdependencies |
| License model | Proprietary format tied to KS-Soft HostMonitor (commercial shareware) |
| Released | late 1990s (HostMonitor first released ~1998) |
| Specification | www.ks-soft.net |
HML conversions
Community Q&A
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