effectcraft/docs/scripting-parity.md

Expressions and scripting parity

Last reviewed: 2026-10-12 · Last updated: 2026-10-12 · Change: minor (#include / #target removed from the estimate (landed in #759)) · Target: Adobe After Effects 2026

Expressions and ExtendScript are how After Effects work is automated and how much of it is built: rigs, templates, studio pipelines. They are also what carries over from After Effects today, while .aep projects can't. Architecture: architecture.md §5 and §5a; extension points: plugins.md; overall numbers: target-app-parity.md.

Breadth ≈ 93%, ready ≈ 65% (estimated). The object models are written from Adobe's public Expression Language Reference and Scripting Guide (behaviour only, AGENTS.md §2) and tested with our own scripts; no real-world script library has been run against both apps.

Feature	After Effects 2026	EffectCraft	Status	Evidence / gap
Expression language	JavaScript engine (default) and Legacy ExtendScript	JavaScript (boa) with legacy array maths (value + [10, 0])	good	crates/expr tests; no separate Legacy ExtendScript engine mode
Expression object model	thisComp, thisLayer, wiggle, loopOut, valueAtTime, sampleImage, footage(), text style API…	Same members, from the reference, including propertyGroup(countUp) and a group's propertyIndex for name-independent rigs (#1619)	good	crates/expr/src/tests.rs, tests/property_group.rs; behaviour of edge cases unmeasured (G1)
Expression editing	Inline field, error bar, pick whip, Expression Language menu, external editors	Inline field that grows, error bar, pick whips (property and value), language menu	partial	External editor support (#364)
Expression performance	Cached, multi-frame	Per-thread boa contexts	unknown	No benchmark
Scripting object model	app, Project, items, layers, properties, keys, eases, render queue, TextDocument, Shape, markers, File/Folder, Socket, app.settings	Same classes, edits run through undoable engine commands; match names table; layers, groups and properties are callable (layer("Effects")(1) is .property(...))	good	crates/script tests (≈ 10 test files)
$.evalFile, BridgeTalk	Evaluate another script file; identify the host application and message other Adobe applications	$.evalFile evaluates a file relative to the calling file (nested at most 32 deep, under the scripts' file gate) and returns its last value; BridgeTalk names the host honestly (appName effectcraft, its version); messaging other applications throws "not supported"	partial	tests_evalfile.rs (#760); no inter-application messaging
ScriptUI	Dialogs, palettes, dockable panels, resource strings, onDraw / ScriptUIGraphics, mouse events	Same, dockable panels reopen at launch	good	ui_scriptui, tests_ui*
app.scheduleTask / cancelTask	One-shot and repeating tasks (polling, panel refresh) until cancelTask	Same: repeating tasks run every delay ms (at least 50 ms, at most 64 pending per script) until cancelTask, until they throw (reported once, then cancelled), or until their owner goes: a script's last window closing, or the project closing for scripts without windows; frontends tick them every frame, agents with script.runTasks	good	tests_tasks.rs (#773); one-shot tasks of a script file still run right after it, not after their delay
Scripts menu, ScriptUI Panels folder	yes	yes	same	plugins.md
Startup / Shutdown folders	yes	not run	missing	plugins.md
#include, #target directives	yes	#include / //@include / #includepath inline files relative to the including script (once each, nested at most 32 deep, under the scripts' file gate; errors name the included file and line); #target, #targetengine, #strict are ignored	good	tests_include.rs (#759); installed scripts and panels have no folder of their own, so they include from the project's folder or absolute paths
.jsxbin	yes	no	out of scope	No public specification
Keyboard shortcuts for scripts	yes: the scripts of the Scripts folder take keys, by their place in the alphabetical list	Edit ▸ Keyboard Shortcuts lists the scripts of File ▸ Scripts; a key stays with the script's file name	same	file_scripts_entries_take_keyboard_shortcuts, a_key_given_to_a_script_runs_it (plugins.md); ScriptUI panels in the Window menu take no key
Command-line rendering aerender	yes	effectcraft-cli render, script, exec	same purpose	apps/effectcraft-cli
Essential Graphics scripting hooks	addToMotionGraphicsTemplate…	yes (M13.7)	good	—
Agent control (MCP, control channel, every command)	none	yes	beyond	agents.md, control-protocol.md; list_effects omits parameter types and ranges (#441)
Real-world script corpus	—	none run	gap	Run popular free scripts (the 11 sample scripts After Effects ships are a good start, run as behaviour tests, never copied)

Estimate

≈ 20–40 h: #include / #target (landed, #759) and Startup / Shutdown folders 4–8 h as first estimated (Startup / Shutdown remain), script shortcuts 2–4 h, a corpus of public scripts and expressions with the fixes it finds 10–20 h, an expression performance benchmark 4–8 h.

Revision history

Date	Change	Summary
2026-10-16	minor	Expression object model row names propertyGroup() and a group's propertyIndex (#1619)
2026-10-12	minor	Estimate no longer counts #include / #target (#759, tests_include.rs); the table row was already current
2026-10-10	major	First expressions and scripting checklist