How it works

Revit compatibility

The add-in targets the lowest stable Revit API build available for each supported year for compatibility with every patch of that year. Both add-in hosts use the .NET 8 logging packages, which also support .NET Framework 4.8 for Revit 2022-2024. The Modern host references Microsoft.Extensions.Logging.Abstractions assembly version 8.0.0.0 and uses System.Diagnostics.DiagnosticSource from Revit 2025-2026's .NET 8 runtime. The logging dependencies avoid higher-version conflicts with the runtime's preloaded System.Diagnostics.DiagnosticSource assembly.

Discovery

The built-in catalog is empty. DevPluginStatusService combines packages with registered plugins. It selects the highest compatible numeric release version, using assembly version and creation time as fallbacks. Each declared command receives one of the slots defined by DevPluginRegistry.CommandSlotCount. Application plugins do not consume command slots.

DevUpdateSourceService reads the configured feed. It adds local packages when useLocalUpdatesFallback=true. It also scans local packages when the feed is absent or fails, even when that setting is false. At window startup, cached rows can include local packages when the cached feed has no entries. A duplicate plugin and release pair prefers the feed entry.

Cache and verification

DevUpdateFeedReader accepts file paths, file URIs, HTTP, HTTPS and GitHub release URIs. GitHub downloads use the locally authenticated gh executable. The GitHub feed reader can reuse a cached asset after a download failure. HTTP and local feed reads do not use that GitHub cache path.

DevUpdatePackageCache prepares a local package before installation. It rejects a size mismatch when the advertised size is positive. It rejects a SHA-256 mismatch when a hash is present. An absent hash disables the hash check. The check covers the archive bytes and does not authenticate the publisher.

Downloaded packages are stored under %LOCALAPPDATA%\RevitDevLoader\cache. Existing cached packages are verified again before use. The default local layout is:

%LOCALAPPDATA%\RevitDevLoader\
  settings.properties
  updates\*.zip
  test-feed\feed.json
  cache\<pluginId>\<pluginId>-DevPayload-<releaseId>.zip
  cache\github-release\<owner_repo>\<tag>\<asset>
  plugins\<pluginId>.devmanifest
  plugins\<pluginId>\runs\<releaseId>\<year>\
  Logs\DevLoader-<date>.log

The GitHub feed cache replaces slashes in repository and tag names with underscores. test-feed is a configurable path, not an automatically selected source. Local packages are read at their original path and are not copied into the download cache.

Installation and registry

DevPayloadInstaller reads root plugin.json from a v2 ZIP, or legacy release-info.properties when JSON is absent. It checks that every requested Revit year has the declared main assembly. For v2, it replaces the first year component in entry.assembly with the requested year. For example, 2026/HelloPlugin.dll selects 2025/HelloPlugin.dll in Revit 2025, with no cross-year fallback. Icons and the original plugin.json are retained beside the installed year folders. Files are extracted into:

%LOCALAPPDATA%\RevitDevLoader\plugins\<pluginId>\runs\<releaseId>\<year>\

If the release folder already exists, the installer tries suffixes from -r2 through -r999. An existing run is never selected as the destination for a new install. These run folders are immutable by installation convention. They are ordinary writable directories on disk.

The registry stores <pluginId>.devmanifest beside the plugin directories. Its key-value content records the command slot, run path and assembly path for each installed year. Registry writes use a temporary sibling file followed by a move or replacement. A failed extraction can leave a partial run directory. The whole installation is not a filesystem transaction.

Application payloads also create %APPDATA%\Autodesk\Revit\Addins\<year>\<pluginId>.addin. The application identity is derived from the plugin ID with SHA-256. An existing manifest is replaceable only when its assembly path points into the managed plugin directory. Application loading takes effect on the next Revit start.

Path checks

Extraction normalizes ZIP entry separators and resolves each destination to a full path. The destination must begin with the full extraction root plus a directory separator. An entry that escapes the extraction root throws DevManifestException. Plugin IDs and release IDs are checked for invalid filename characters and separators. The package cache also checks its resulting path against the cache root.

These checks apply to the paths shown in the implementation. They are not a sandbox for loaded code. Feeds, local settings and payload assemblies must come from trusted sources.

Ribbon generation

The host creates the DevLoader panel under Add-Ins with only the Dev manager button when nothing is installed. At startup and after installation, it reads registered manifests and creates one pushbutton per installed command. commands[].text, tooltip and icon supply presentation; the package icon is the fallback for an omitted command icon. The 32px image supplies LargeImage; an optional @16.png sibling supplies Image. Application packages have no command buttons. The feed publisher exports the same package icon bytes for uninstalled catalog rows.

Updates preserve command IDs and their slots, rebind current metadata and hide commands removed from the package. The runner resolves the selected slot's class and current assembly path on every click. Uninstall hides and disables all buttons for the package; the Revit API cannot remove ribbon items. Reinstall reuses existing button identities. The fixed host provides 20 slots across all installed commands. See plugin packages for format and rendering rules.

Command loading

RunPluginCommandBase resolves its slot through the registry. ShadowCopyCommandRunner attaches an assembly resolver for the command call. The main assembly is loaded from its run path with Assembly.LoadFile. Dependencies are resolved from the same directory when the runtime invokes that resolver. The runner creates the declared command type and invokes its public Execute method. It removes the resolver after the call.

The loader does not unload assemblies or clear plugin static state. Dependency identity conflicts and conventional installations can still require a Revit restart. The manager detects matching conventional .addin files and displays a warning.

Retention and removal

The manager passes runRetentionCount to the installer. The default is three runs. Cleanup preserves the current run when it exists and fills the remaining retention slots by directory modification time. Equal timestamps are ordered by folder name. The limit applies to all runs of a plugin, not separately to each Revit year; older runs referenced by another installed year are not separately protected. Deletion failures are reported as skipped folders.

Removing a plugin deletes its registry entry and hides its command button. For application payloads, removal deletes owned .addin files. It preserves a manifest that points outside the managed plugin directory. Removal does not unload code already present in Revit or delete all old run folders.

Logs

Logs are written under %LOCALAPPDATA%\RevitDevLoader\Logs. The logger falls back to a temporary directory if that folder is unavailable. Files roll daily and at 10 MiB, with a retention limit of 14 files. Log messages can contain local paths and feed locations.