Steam Version Compatibility

OpenSteamTool no longer ships byte-pattern signatures inside the DLL. Instead, it dynamically resolves Steam's internal API offsets at runtime using a pattern-matching system.

How It Works

On each launch, OpenSteamTool:

1. Computes SHA-256 of steamclient64.dll and steamui.dll on disk
2. Looks up a matching pattern file (TOML) from the upstream tracker
3. Resolves function addresses using the pattern data
4. Applies the resolved offsets to hook Steam's internal APIs

Pattern Resolution

Each pattern TOML contains PatternEntry records with the following fields:

Field	Description
name	Human-readable function name (e.g., "BBuildAndAsyncSendFrame")
rva	Relative Virtual Address — if provided, the address is calculated by adding this offset to the module base, bypassing the need for a scan
sig	IDA-style hex byte pattern (e.g., 48 89 ? ? 57 48 81 ? ? ? ? ?) used as a fallback if the RVA is absent or invalid

The resolution order is:

1. RVA lookup — fastest, direct offset calculation
2. Signature scan — sliding-window comparison against the module's memory, with ?? as wildcards for bytes that change between builds

Function names are looked up using FNV-1a hashing for efficient map access.

Error Handling

If a pattern TOML fails to download (e.g., HTTP 404), the module is added to g_failedModules and a popup informs the user. If specific functions within a successfully loaded module cannot be found, they're tracked in g_missingFunctions and reported after all hooks have attempted to install. OST continues working — only the hooks tied to missing functions are disabled.

Lookup Order

Every launch, OST checks the following sources in order:

GitHub Raw ──> jsDelivr CDN ──> Local Cache

1. GitHub Raw (Canonical)

https://raw.githubusercontent.com/OpenSteam001/steam-monitor/pattern/...

This is the primary, canonical source. The repository is OpenSteam001/steam-monitor (pattern branch).

2. jsDelivr CDN (Automatic Fallback)

If GitHub raw is unreachable (connection refused, timeout, or 5xx error), OST automatically falls back to the jsDelivr CDN. No configuration required.

This is especially useful in regions where raw.githubusercontent.com is blocked but jsDelivr is reachable (e.g., mainland China).

3. Local Cache (When Offline)

<Steam>/opensteamtool/pattern/<subdir>/<sha256>.toml

The local cache is used only when both remote sources are unreachable. It is overwritten after every successful remote fetch.

Important Behaviors

Behavior	Details
Remote check every launch	OST consults remote mirrors on every launch, so you automatically pick up upstream updates (new signatures, fixes) without clearing any cache
404 stops the chain	If any mirror returns HTTP 404, the lookup stops immediately — all mirrors serve the same content, so a 404 means the upstream bot hasn't published a TOML for this Steam build yet
Graceful degradation	If no pattern is found, only the hooks tied to that DLL are disabled. The rest of OST keeps working
Minimal network impact	Outbound HTTPS request per DLL (~10 KB each), runs on a worker thread — never blocks Steam's loader

404 Fallback Behavior

When a 404 occurs:

1. OST falls back to the local cache (if one exists)
2. Otherwise, a one-shot popup appears with:
   • The unmatched DLL name
   • Its SHA-256 hash
   • The expected cache path
   • The upstream URL
3. Only the hooks for that DLL are disabled — OST continues working for everything else

Manual Cache

You can drop a pattern TOML into the cache directory manually:

<Steam>/opensteamtool/pattern/<subdir>/<sha256>.toml

The file name must be <sha256>.toml. The cache fallback will pick it up the next time remote sources are unreachable.

Using a Custom Mirror

For most users, the built-in GitHub → jsDelivr fallback is sufficient. To use a private mirror or intranet server, configure a full URL template in opensteamtool.toml:

[remote]
url_template = "https://your.server/{channel}/{component}/{sha256}.toml"

Template Placeholders

Placeholder	Description	Current Values
{channel}	Content channel	pattern, ipc
{component}	DLL component name	steamclient64, steamui
{sha256}	SHA-256 hash of the DLL	Hex string

Example: jsDelivr Template

[remote]
url_template = "https://fast.jsdelivr.net/gh/OpenSteam001/steam-monitor@{channel}/{component}/{sha256}.toml"

Custom Mirror Behavior

• A custom mirror replaces the built-in remote sources (GitHub + jsDelivr)
• Local cache fallback remains available
• All three placeholders are required in the template

Runtime Requirements

• Outbound HTTPS access to raw.githubusercontent.com on first launch after a Steam update
• After the first successful fetch, patterns are cached locally
• Subsequent launches are fast even without network access (cached patterns are used) cached)

Having Compatibility Issues?

Check the FAQ page for solutions to "Unsupported Steam version" and "No pattern found" errors.