diff --git a/src/classes/MsgInterface/MsgInterface.ts b/src/classes/MsgInterface/MsgInterface.ts
index 512eccc..3a74ae4 100644
--- a/src/classes/MsgInterface/MsgInterface.ts
+++ b/src/classes/MsgInterface/MsgInterface.ts
@@ -1,7 +1,15 @@
-type NoteTypes =  'DESCRIPTION' | 'AUTHORSHIP' | 'PARAMETERS' | 'CONTEXT' | 'COMMENT';
+/**
+ * Categories of notes that can be attached to a message or resource.
+ */
+export type NoteTypes = 'DESCRIPTION' | 'AUTHORSHIP' | 'PARAMETERS' | 'CONTEXT' | 'COMMENT';
 
+/**
+ * A free-form note attached to a message or resource for translators and tools.
+ */
 export type MsgNote = {
+  /** What kind of note this is. */
   type: NoteTypes
+  /** The note text. */
   content: string;
 }
 
@@ -20,20 +28,35 @@ export type MsgFormat = 'MF1' | 'MF2' | 'NONE';
  */
 export const MSG_DEFAULT_FORMAT: MsgFormat = 'MF2';
 
+/**
+ * Locale and formatting metadata shared by messages and resources.
+ */
 export type MsgAttributes = {
+  /** BCP 47 language tag for the content (for example, `en` or `zh-Hans`). */
   lang?: string
+  /** Text direction: typically `ltr`, `rtl`, or `auto`. */
   dir?: string
+  /** When true, the content should not be translated (Do Not Translate). */
   dnt?: boolean
+  /** MessageFormat syntax used by the string, if any. */
   format?: MsgFormat
 }
 
+/**
+ * Default attribute values applied when none are provided.
+ */
 export const DEFAULT_ATTRIBUTES: MsgAttributes = {
   lang: 'und',
   dir: 'auto',
   dnt: false
 }
 
+/**
+ * Shared shape for objects that carry attributes and translator notes.
+ */
 export interface MsgInterface {
+  /** Locale and formatting metadata. */
   attributes: MsgAttributes
+  /** Notes for translators and tooling. */
   notes: MsgNote[]
 }
diff --git a/src/classes/MsgMessage/MsgMessage.ts b/src/classes/MsgMessage/MsgMessage.ts
index d637f38..1c75254 100644
--- a/src/classes/MsgMessage/MsgMessage.ts
+++ b/src/classes/MsgMessage/MsgMessage.ts
@@ -2,13 +2,25 @@ import { MessageFormat, type MessageFormatOptions } from "messageformat";
 import { mf1ToMessage } from "@messageformat/icu-messageformat-1";
 import { MsgInterface, DEFAULT_ATTRIBUTES, MSG_DEFAULT_FORMAT, type MsgAttributes, type MsgFormat, type MsgNote } from "../MsgInterface/MsgInterface.js";
 
+/**
+ * Plain data used to create a {@link MsgMessage}.
+ */
 export type MsgMessageData = {
+  /** Unique key that identifies this message within a resource. */
   key: string
+  /** The message string, possibly in MessageFormat syntax. */
   value: string
+  /** Optional locale and formatting metadata. */
   attributes?: MsgAttributes;
+  /** Optional notes for translators and tooling. */
   notes?: MsgNote[]
 }
 
+/**
+ * A single localizable message with a key, value, attributes, and notes.
+ *
+ * Supports MessageFormat 1, MessageFormat 2, and unformatted (`NONE`) strings.
+ */
 export class MsgMessage implements MsgInterface {
   private _key: string;
   private _value: string;
@@ -16,6 +28,9 @@ export class MsgMessage implements MsgInterface {
   private _attributes: MsgAttributes;
   private _notes: MsgNote[] = [];
 
+  /**
+   * Creates a message from its parts. Prefer {@link MsgMessage.create}.
+   */
   private constructor(key: string, value: string, attributes?: MsgAttributes, notes?: MsgNote[]) {
     this._key = key;
     this._value = value;
@@ -30,28 +45,38 @@ export class MsgMessage implements MsgInterface {
 
   }
 
+  /**
+   * Builds a message from {@link MsgMessageData}.
+   */
   static create(data: MsgMessageData) {
     const { key, value, attributes, notes } = data;
     const message = new MsgMessage(key, value, attributes, notes);
     return message;
   }
 
+  /** Unique key that identifies this message within a resource. */
   public get key() {
     return this._key;
   }
 
+  /** The message string, possibly in MessageFormat syntax. */
   public get value() {
     return this._value;
   }
 
+  /** Locale and formatting metadata for this message. */
   public get attributes() {
     return this._attributes;
   }
 
+  /** Notes attached to this message for translators and tooling. */
   public get notes() {
     return this._notes;
   }
 
+  /**
+   * Appends a note to this message.
+   */
   public addNote(note: MsgNote) {
     this.notes.push(note);
   }
@@ -63,6 +88,9 @@ export class MsgMessage implements MsgInterface {
     return this.attributes.format ?? MSG_DEFAULT_FORMAT;
   }
 
+  /**
+   * Returns a cached MessageFormat formatter for this message's value.
+   */
   private getFormatter(options?: MessageFormatOptions): MessageFormat {
     if (!this._mf) {
       this._mf = this.resolveFormat() === 'MF1'
@@ -72,6 +100,11 @@ export class MsgMessage implements MsgInterface {
     return this._mf;
   }
 
+  /**
+   * Formats the message with the given placeholder data.
+   *
+   * For `NONE` format messages, returns the raw value unchanged.
+   */
   public format(data: Record<string, any>, options?: MessageFormatOptions) {
     // NONE messages are not formatted; the raw string is returned as-is.
     if (this.resolveFormat() === 'NONE') {
@@ -80,6 +113,11 @@ export class MsgMessage implements MsgInterface {
     return this.getFormatter(options).format(data);
   }
 
+  /**
+   * Formats the message into structured parts with the given placeholder data.
+   *
+   * For `NONE` format messages, returns a single text part with the raw value.
+   */
   public formatToParts(data: Record<string, any>, options?: MessageFormatOptions) {
     // NONE messages have no placeholders to resolve; return the raw text part.
     if (this.resolveFormat() === 'NONE') {
@@ -88,6 +126,11 @@ export class MsgMessage implements MsgInterface {
     return this.getFormatter(options).formatToParts(data);
   }
 
+  /**
+   * Returns a plain data object for this message.
+   *
+   * @param stripNotes - When true, notes are omitted from the result.
+   */
   public getData(stripNotes: boolean = false) {
     return {
       key: this.key,
@@ -97,10 +140,18 @@ export class MsgMessage implements MsgInterface {
     }
   }
 
+  /**
+   * Returns the message value as a string.
+   */
   public toString() {
     return this.value;
   }
 
+  /**
+   * Serializes this message to a formatted JSON string.
+   *
+   * @param stripNotes - When true, notes are omitted from the serialized data.
+   */
   public toJSON(stripNotes: boolean = false) {
     return JSON.stringify(this.getData(stripNotes), null, 2);
   }
diff --git a/src/classes/MsgProject/MsgProject.ts b/src/classes/MsgProject/MsgProject.ts
index 4cec1ec..74c93ad 100644
--- a/src/classes/MsgProject/MsgProject.ts
+++ b/src/classes/MsgProject/MsgProject.ts
@@ -1,36 +1,66 @@
 import { type MsgResourceData } from "../MsgResource/MsgResource.js";
 import { type MsgFormat, MSG_DEFAULT_FORMAT } from "../MsgInterface/MsgInterface.js";
 
-type MsgProjectSettings = {
+/**
+ * Project-level settings such as name, version, and default message format.
+ */
+export type MsgProjectSettings = {
+  /** Display name of the localization project. */
   name: string
+  /** Optional project version number. */
   version?: number
+  /** Default message format inherited by resources and messages. */
   format?: MsgFormat
 };
 
-type MsgTargetLocalesSettings = {
+/**
+ * Map of a requested locale to the chain of locales used to load translations.
+ */
+export type MsgTargetLocalesSettings = {
   [key: string]: string[]
 }
 
-type MsgLocalesSettings = {
+/**
+ * Locale configuration for a project: source, pseudo, and target locales.
+ */
+export type MsgLocalesSettings = {
+  /** Locale of the source (authoring) strings. */
   sourceLocale: string
+  /** Locale used for pseudo-localization during development. */
   pseudoLocale: string
+  /** Target locales and their fallback load chains. */
   targetLocales: MsgTargetLocalesSettings
 };
 
+/**
+ * Async function that loads translated resource data for a project, title, and language.
+ */
 export type MsgTranslationLoader = (project: string, title: string, lang: string) => Promise<MsgResourceData>;
 
+/**
+ * Plain data used to create a {@link MsgProject}.
+ */
 export type MsgProjectData = {
+  /** Project name, version, and default format. */
   project: MsgProjectSettings
+  /** Source, pseudo, and target locale settings. */
   locales: MsgLocalesSettings
+  /** Function used to load translations for a locale. */
   loader: MsgTranslationLoader
 };
 
+/**
+ * Default project settings applied when none are provided.
+ */
 const defaultProjectSettings: MsgProjectSettings = {
   name: 'messages',
   version: 1,
   format: MSG_DEFAULT_FORMAT
 };
 
+/**
+ * Default locale settings applied when none are provided.
+ */
 const defaultLocalesSettings: MsgLocalesSettings = {
   sourceLocale: 'en',
   pseudoLocale: 'en-XA',
@@ -39,16 +69,31 @@ const defaultLocalesSettings: MsgLocalesSettings = {
   }
 };
 
+/**
+ * A localization project that holds settings, locales, and a translation loader.
+ *
+ * Resources are created against a project so they can inherit format defaults
+ * and load translations through the project's loader.
+ */
 export class MsgProject {
+  /** Project name, version, and default format. */
   _project: MsgProjectSettings;
+  /** Source, pseudo, and target locale settings. */
   _locales: MsgLocalesSettings;
+  /** Function used to load translations for a locale. */
   _loader: MsgTranslationLoader;
 
+  /**
+   * Builds a project from {@link MsgProjectData}.
+   */
   static create(data: MsgProjectData) {
     const { project, locales, loader } = data;
     return new MsgProject(project, locales, loader);
   }
 
+  /**
+   * Creates a project from its settings and loader. Prefer {@link MsgProject.create}.
+   */
   private constructor(
     projectSettings: MsgProjectSettings,
     localesSettings: MsgLocalesSettings,
@@ -59,14 +104,17 @@ export class MsgProject {
     this._loader = loader;
   }
 
+  /** Project name, version, and default format. */
   public get project() {
     return this._project;
   }
 
+  /** Source, pseudo, and target locale settings. */
   public get locales() {
     return this._locales;
   }
 
+  /** Function used to load translations for a locale. */
   public get loader() {
     return this._loader;
   }
@@ -79,6 +127,9 @@ export class MsgProject {
     return this._project.format ?? MSG_DEFAULT_FORMAT;
   }
 
+  /**
+   * Returns the translation load chain for a locale, or `undefined` if unsupported.
+   */
   public getTargetLocale(locale: string): string[] | undefined {
     return this._locales.targetLocales[locale];
   }
diff --git a/src/classes/MsgResource/MsgResource.ts b/src/classes/MsgResource/MsgResource.ts
index 24e88b8..849f9a2 100644
--- a/src/classes/MsgResource/MsgResource.ts
+++ b/src/classes/MsgResource/MsgResource.ts
@@ -4,13 +4,26 @@ import { type MsgMessageData, MsgMessage } from "../MsgMessage/MsgMessage.js";
 import { DEFAULT_ATTRIBUTES, MSG_DEFAULT_FORMAT, MsgInterface, type MsgAttributes, type MsgNote } from "../MsgInterface/MsgInterface.js";
 import { MsgProject } from "../MsgProject/MsgProject.js";
 
+/**
+ * Plain data used to create or describe a {@link MsgResource}.
+ */
 export type MsgResourceData = {
+  /** Title that identifies this resource within a project. */
   title: string
+  /** Locale and formatting metadata for the resource. */
   attributes: MsgAttributes
+  /** Optional notes for translators and tooling. */
   notes?: MsgNote[]
+  /** Optional list of messages in this resource. */
   messages?: MsgMessageData[]
 }
 
+/**
+ * A named collection of messages belonging to a {@link MsgProject}.
+ *
+ * Resources inherit format defaults from their project, support translation
+ * loading (including pseudo-localization), and can serialize to plain data.
+ */
 export class MsgResource extends Map<string, MsgMessage> implements MsgInterface {
 
   private _attributes: MsgAttributes = {};
@@ -19,6 +32,12 @@ export class MsgResource extends Map<string, MsgMessage> implements MsgInterface
 
   private _project: MsgProject;
 
+  /**
+   * Builds a resource from {@link MsgResourceData} and an owning project.
+   *
+   * When `messages` is provided, each entry is added to the resource.
+   * When omitted, the resource starts empty.
+   */
   static create(data: MsgResourceData, project: MsgProject ) {
     const { title, attributes, notes, messages}  = data;
     const res = new MsgResource(title, attributes, project, notes);
@@ -35,6 +54,9 @@ export class MsgResource extends Map<string, MsgMessage> implements MsgInterface
     return res;
   }
 
+  /**
+   * Creates a resource bound to a project. Prefer {@link MsgResource.create}.
+   */
   private constructor (title: string, attributes: MsgAttributes, project: MsgProject, notes?: MsgNote[]) {
     super();
     this._title = title;
@@ -49,6 +71,9 @@ export class MsgResource extends Map<string, MsgMessage> implements MsgInterface
 
   }
 
+  /**
+   * Returns true when the message's attributes match this resource's attributes.
+   */
   private hasMatchingAttributes(message: MsgMessage): boolean {
     const res = this.attributes;
     const msg = message.attributes;
@@ -58,10 +83,16 @@ export class MsgResource extends Map<string, MsgMessage> implements MsgInterface
       && this.resolveFormat(res) === this.resolveFormat(msg);
   }
 
+  /**
+   * Resolves a format from attributes, falling back to the library default.
+   */
   private resolveFormat(attributes: MsgAttributes) {
     return attributes.format ?? MSG_DEFAULT_FORMAT;
   }
 
+  /**
+   * Pseudo-localizes an MF2 message by localizing only literal text parts.
+   */
   private pseudoLocalizeMF2(
     source: string,
     options?: { strategy?: "accented" | "bidi" }
@@ -82,38 +113,55 @@ export class MsgResource extends Map<string, MsgMessage> implements MsgInterface
     return stringifyMessage(msg);
   }
 
+  /** Locale and formatting metadata for this resource. */
   public get attributes() {
     return this._attributes;
   }
 
+  /** Replaces the resource's locale and formatting metadata. */
   public set attributes(attributes: MsgAttributes) {
     this._attributes = attributes;
   }
   
+  /** Notes attached to this resource for translators and tooling. */
   public get notes() {
     return this._notes;
   }
 
+  /** Replaces the notes attached to this resource. */
   public set notes(notes: MsgNote[]) {
     this._notes = notes;
   }
 
+  /**
+   * Appends a note to this resource.
+   */
   public addNote(note: MsgNote) {
     this.notes.push(note);
   }
 
+  /** Title that identifies this resource within a project. */
   public get title() {
    return this._title;
   }
   
+  /** Sets the title that identifies this resource within a project. */
   public set title(title: string) {
     this._title = title;
   }
 
+  /**
+   * Returns the project this resource belongs to.
+   */
   public getProject(): MsgProject {
     return this._project;
   }
 
+  /**
+   * Adds a message to this resource, merging resource attributes with any overrides.
+   *
+   * @returns This resource, for chaining.
+   */
   public add(key: string, value: string, attributes?: MsgAttributes, notes?: MsgNote[]) {
 
     const merged = {...this.attributes, ...attributes};
@@ -128,6 +176,14 @@ export class MsgResource extends Map<string, MsgMessage> implements MsgInterface
     return this;
   }
 
+  /**
+   * Builds a translated copy of this resource from translation data.
+   *
+   * Messages present in the translation replace the source; missing keys keep
+   * the source message. Notes are carried over from the source.
+   *
+   * @throws {TypeError} When the translation title does not match this resource.
+   */
   public translate(data: MsgResourceData) {
     const {title, attributes, messages} = data;
 
@@ -183,6 +239,14 @@ export class MsgResource extends Map<string, MsgMessage> implements MsgInterface
     return { ...attributes, format };
   }
 
+  /**
+   * Loads and applies translations for a locale via the project loader.
+   *
+   * When `lang` is the project's pseudo-locale, returns a pseudo-localized
+   * copy without calling the loader.
+   *
+   * @throws {Error} When the locale is unsupported or its language chain is empty.
+   */
   public async getTranslation(lang: string) {
 
     const project = this._project;
@@ -227,6 +291,14 @@ export class MsgResource extends Map<string, MsgMessage> implements MsgInterface
     return translated;
   }
 
+  /**
+   * Returns a plain data object for this resource and its messages.
+   *
+   * Attributes that match the resource or project defaults are omitted where
+   * possible to keep the output compact.
+   *
+   * @param stripNotes - When true, notes are omitted from the result.
+   */
   public getData(stripNotes: boolean = false): MsgResourceData {
 
     const resourceFormat = this.resolveFormat(this.attributes);
@@ -267,8 +339,13 @@ export class MsgResource extends Map<string, MsgMessage> implements MsgInterface
     }
   }
 
+  /**
+   * Serializes this resource to a formatted JSON string.
+   *
+   * @param stripNotes - When true, notes are omitted from the serialized data.
+   */
   public toJSON(stripNotes: boolean = false) {
     return JSON.stringify(this.getData(stripNotes), null, 2);
   }
   
-}
\ No newline at end of file
+}
diff --git a/src/classes/index.ts b/src/classes/index.ts
index 73076eb..c69f90a 100644
--- a/src/classes/index.ts
+++ b/src/classes/index.ts
@@ -1,3 +1,6 @@
+/**
+ * Barrel export for the public msg classes and shared types.
+ */
 export * from './MsgInterface/MsgInterface.js';
 export * from './MsgMessage/MsgMessage.js';
 export * from './MsgResource/MsgResource.js';
diff --git a/src/index.ts b/src/index.ts
index ae2aaf6..4771dfb 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1 +1,7 @@
-export * from './classes/index.js';
\ No newline at end of file
+/**
+ * @worldware/msg — message localization tooling.
+ *
+ * Re-exports the public classes, types, and constants for building projects,
+ * resources, and messages.
+ */
+export * from './classes/index.js';