fvtt-dev

This skill should be used when creating or applying Active Effects, working with effect changes and modes (ADD, MULTIPLY, OVERRIDE, CUSTOM), implementing duration tracking for combat, or handling effect transfer from items to actors.

This skill should be used when creating custom windows with ApplicationV2, building forms with FormApplication, using Dialog for prompts, understanding the render lifecycle, or migrating from Application v1 to ApplicationV2.

This skill should be used when working with the Foundry canvas, PIXI.js rendering, canvas layers, placeable objects (tokens, tiles, drawings), render flags for performance, or canvas lifecycle hooks like canvasReady.

This skill should be used when creating chat messages, sending roll results to chat, configuring speakers, implementing whispers and roll modes, or hooking into chat message rendering.

This skill should be used when working with the Combat tracker, Combatant documents, initiative rolling and sorting, turn/round management, or implementing combat hooks like combatStart, combatTurn, and combatRound.

This skill should be used when creating compendium packs, registering packs in manifests, importing/exporting documents, querying pack contents, or using the CLI for pack management and version control workflows.

This skill should be used when moving data between storage locations, changing data structures, renaming fields, or removing deprecated data. Covers schema versioning, safe migration methods, the Foundry unset operator, and idempotent migrations.

This skill should be used when choosing between flags, settings, or files for data storage, implementing document flags, registering module settings, handling file uploads, or migrating data between storage types. Covers namespacing, scope types, and performance optimization.

This skill should be used when implementing dice rolling, creating Roll formulas, sending rolls to chat with toMessage, preparing getRollData, creating custom dice types, or handling roll modifiers like advantage/disadvantage. Covers Roll class, evaluation, and common patterns.

This skill should be used when adding error handling to catch blocks, standardizing error handling across a codebase, or ensuring proper UX with user messages vs technical logs. Covers NotificationOptions, Hooks.onError, and preventing console noise.

This skill should be used when registering hooks, creating custom hooks for module APIs, debugging hook execution, handling async in hooks, or preventing memory leaks from unclean hook removal. Covers Hooks.on/once/call/callAll, lifecycle order, and common pitfalls.

This skill should be used when implementing internationalization (i18n), creating language files, using game.i18n.localize/format, adding template localization helpers, or following best practices for translatable strings.

This skill should be used when adding features that update actors or items, implementing hook handlers, modifying update logic, or replacing embedded documents. Covers ownership guards, no-op checks, batched updates, queueUpdate wrapper, atomic document operations, and letting Foundry handle renders automatically for multi-client sync.

This skill should be used when creating or extending ActorSheet/ItemSheet classes, implementing getData or _prepareContext, binding events with activateListeners, handling drag/drop, or migrating from ApplicationV1 to ApplicationV2. Covers both legacy V1 and modern V2 patterns.

This skill should be used when implementing multiplayer synchronization, using game.socket.emit/on, creating executeAsGM patterns for privileged operations, broadcasting events between clients, or avoiding common pitfalls like race conditions and duplicate execution.

This skill should be used when the user asks to "migrate to V13", "upgrade to Foundry V13", "update module for V13", "fix V13 compatibility", "convert to ESM", "use DataModel", or mentions V13-specific patterns like hook signature changes, actor.system vs actor.data.data, or Application V2. Provides comprehensive Foundry VTT V13 development patterns and migration guidance.

This skill should be used when importing Foundry classes, registering sheets, loading templates, enriching HTML, or using any Foundry API that has moved to namespaces. Covers compat wrappers, deferred sheet registration, and the modern-first fallback pattern.