diff --git a/api/params.json b/api/params.json
index f53c9014..bb5f47f7 100644
--- a/api/params.json
+++ b/api/params.json
@@ -1,5 +1,11 @@
 {
   "version": "0.5.0",
+  "bottom": {
+    "default": 0,
+    "min": 0,
+    "max": 512,
+    "step": 8
+  },
   "cfg": {
     "default": 6,
     "min": 1,
@@ -18,12 +24,26 @@
     "max": 1,
     "step": 0.1
   },
+  "fillColor": {
+    "default": "#000000",
+    "keys": []
+  },
+  "filter": {
+    "default": "none",
+    "keys": []
+  },
   "height": {
     "default": 512,
     "min": 64,
     "max": 1024,
     "step": 8
   },
+  "left": {
+    "default": 0,
+    "min": 0,
+    "max": 512,
+    "step": 8
+  },
   "model": {
     "default": "stable-diffusion-onnx-v1-5",
     "keys": []
@@ -32,6 +52,10 @@
     "default": "",
     "keys": []
   },
+  "noise": {
+    "default": "histogram",
+    "keys": []
+  },
   "outscale": {
     "default": 1,
     "min": 1,
@@ -46,6 +70,12 @@
     "default": "an astronaut eating a hamburger",
     "keys": []
   },
+  "right": {
+    "default": 0,
+    "min": 0,
+    "max": 512,
+    "step": 8
+  },
   "scale": {
     "default": 1,
     "min": 1,
@@ -74,6 +104,12 @@
     "max": 1,
     "step": 0.01
   },
+  "top": {
+    "default": 0,
+    "min": 0,
+    "max": 512,
+    "step": 8
+  },
   "width": {
     "default": 512,
     "min": 64,
diff --git a/gui/src/client.ts b/gui/src/client.ts
index 54bd49fb..5af6dedf 100644
--- a/gui/src/client.ts
+++ b/gui/src/client.ts
@@ -1,22 +1,36 @@
+/* eslint-disable max-lines */
 import { doesExist } from '@apextoaster/js-utils';
 
 import { ServerParams } from './config.js';
 
+/**
+ * Shared parameters for anything using models, which is pretty much everything.
+ */
 export interface ModelParams {
   /**
-   * Which ONNX model to use.
+   * The diffusion model to use.
    */
   model: string;
 
   /**
-   * Hardware accelerator or CPU mode.
+   * The hardware acceleration platform to use.
    */
   platform: string;
 
+  /**
+   * The upscaling model to use.
+   */
   upscaling: string;
+
+  /**
+   * The correction model to use.
+   */
   correction: string;
 }
 
+/**
+ * Shared parameters for most of the image requests.
+ */
 export interface BaseImgParams {
   scheduler: string;
   prompt: string;
@@ -27,20 +41,25 @@ export interface BaseImgParams {
   seed: number;
 }
 
-export interface Img2ImgParams extends BaseImgParams {
-  source: Blob;
-  strength: number;
-}
-
-export type Img2ImgResponse = Required<Omit<Img2ImgParams, 'file'>>;
-
+/**
+ * Parameters for txt2img requests.
+ */
 export interface Txt2ImgParams extends BaseImgParams {
   width?: number;
   height?: number;
 }
 
-export type Txt2ImgResponse = Required<Txt2ImgParams>;
+/**
+ * Parameters for img2img requests.
+ */
+export interface Img2ImgParams extends BaseImgParams {
+  source: Blob;
+  strength: number;
+}
 
+/**
+ * Parameters for inpaint requests.
+ */
 export interface InpaintParams extends BaseImgParams {
   mask: Blob;
   source: Blob;
@@ -51,6 +70,11 @@ export interface InpaintParams extends BaseImgParams {
   fillColor: string;
 }
 
+/**
+ * Additional parameters for outpaint border.
+ *
+ * @todo should be nested under inpaint/outpaint params
+ */
 export interface OutpaintPixels {
   enabled: boolean;
 
@@ -60,14 +84,27 @@ export interface OutpaintPixels {
   bottom: number;
 }
 
+/**
+ * Parameters for outpaint requests.
+ */
 export type OutpaintParams = InpaintParams & OutpaintPixels;
 
+/**
+ * Additional parameters for the inpaint brush.
+ *
+ * These are not currently sent to the server and only stored in state.
+ *
+ * @todo move to state
+ */
 export interface BrushParams {
   color: number;
   size: number;
   strength: number;
 }
 
+/**
+ * Additional parameters for upscaling.
+ */
 export interface UpscaleParams {
   enabled: boolean;
 
@@ -78,10 +115,16 @@ export interface UpscaleParams {
   faceStrength: number;
 }
 
+/**
+ * Parameters for upscale requests.
+ */
 export interface UpscaleReqParams {
   source: Blob;
 }
 
+/**
+ * General response for most image requests.
+ */
 export interface ImageResponse {
   output: {
     key: string;
@@ -94,10 +137,16 @@ export interface ImageResponse {
   };
 }
 
+/**
+ * Status response from the ready endpoint.
+ */
 export interface ReadyResponse {
   ready: boolean;
 }
 
+/**
+ * List of available models.
+ */
 export interface ModelsResponse {
   diffusion: Array<string>;
   correction: Array<string>;
@@ -105,50 +154,103 @@ export interface ModelsResponse {
 }
 
 export interface ApiClient {
+  /**
+   * List the available filter masks for inpaint.
+   */
   masks(): Promise<Array<string>>;
+
+  /**
+   * List the available models.
+   */
   models(): Promise<ModelsResponse>;
+
+  /**
+   * List the available noise sources for inpaint.
+   */
   noises(): Promise<Array<string>>;
+
+  /**
+   * Get the valid server parameters to validate image parameters.
+   */
   params(): Promise<ServerParams>;
+
+  /**
+   * Get the available hardware acceleration platforms.
+   */
   platforms(): Promise<Array<string>>;
+
+  /**
+   * List the available pipeline schedulers.
+   */
   schedulers(): Promise<Array<string>>;
 
-  img2img(model: ModelParams, params: Img2ImgParams, upscale?: UpscaleParams): Promise<ImageResponse>;
+  /**
+   * Start a txt2img pipeline.
+   */
   txt2img(model: ModelParams, params: Txt2ImgParams, upscale?: UpscaleParams): Promise<ImageResponse>;
+
+  /**
+   * Start an im2img pipeline.
+   */
+  img2img(model: ModelParams, params: Img2ImgParams, upscale?: UpscaleParams): Promise<ImageResponse>;
+
+  /**
+   * Start an inpaint pipeline.
+   */
   inpaint(model: ModelParams, params: InpaintParams, upscale?: UpscaleParams): Promise<ImageResponse>;
+
+  /**
+   * Start an outpaint pipeline.
+   */
   outpaint(model: ModelParams, params: OutpaintParams, upscale?: UpscaleParams): Promise<ImageResponse>;
+
+  /**
+   * Start an upscale pipeline.
+   */
   upscale(model: ModelParams, params: UpscaleReqParams, upscale?: UpscaleParams): Promise<ImageResponse>;
 
+  /**
+   * Check whether some pipeline's output is ready yet.
+   */
   ready(params: ImageResponse): Promise<ReadyResponse>;
 }
 
-export const STATUS_SUCCESS = 200;
-
-export function paramsFromConfig(defaults: ServerParams): Required<BaseImgParams> {
-  return {
-    cfg: defaults.cfg.default,
-    negativePrompt: defaults.negativePrompt.default,
-    prompt: defaults.prompt.default,
-    scheduler: defaults.scheduler.default,
-    steps: defaults.steps.default,
-    seed: defaults.seed.default,
-  };
-}
-
+/**
+ * Fixed precision for integer parameters.
+ */
 export const FIXED_INTEGER = 0;
+
+/**
+ * Fixed precision for float parameters.
+ *
+ * The GUI limits the input steps based on the server parameters, but this does limit
+ * the maximum precision that can be sent back to the server, and may have to be
+ * increased in the future.
+ */
 export const FIXED_FLOAT = 2;
+export const STATUS_SUCCESS = 200;
 
 export function equalResponse(a: ImageResponse, b: ImageResponse): boolean {
   return a.output === b.output;
 }
 
+/**
+ * Join URL path segments, which always use a forward slash per https://www.rfc-editor.org/rfc/rfc1738
+ */
 export function joinPath(...parts: Array<string>): string {
   return parts.join('/');
 }
 
+/**
+ * Build the URL to an API endpoint, given the API root and a list of segments.
+ */
 export function makeApiUrl(root: string, ...path: Array<string>) {
   return new URL(joinPath('api', ...path), root);
 }
 
+/**
+ * Build the URL for an image request, including all of the base image parameters.
+ */
 export function makeImageURL(root: string, type: string, params: BaseImgParams): URL {
   const url = makeApiUrl(root, type);
   url.searchParams.append('cfg', params.cfg.toFixed(FIXED_FLOAT));
@@ -172,6 +274,9 @@ export function makeImageURL(root: string, type: string, params: BaseImgParams):
   return url;
 }
 
+/**
+ * Append the model parameters to an existing URL.
+ */
 export function appendModelToURL(url: URL, params: ModelParams) {
   url.searchParams.append('model', params.model);
   url.searchParams.append('platform', params.platform);
@@ -179,6 +284,9 @@ export function appendModelToURL(url: URL, params: ModelParams) {
   url.searchParams.append('correction', params.correction);
 }
 
+/**
+ * Append the upscale parameters to an existing URL.
+ */
 export function appendUpscaleToURL(url: URL, upscale: UpscaleParams) {
   if (upscale.enabled) {
     url.searchParams.append('denoise', upscale.denoise.toFixed(FIXED_FLOAT));
@@ -189,6 +297,9 @@ export function appendUpscaleToURL(url: URL, upscale: UpscaleParams) {
   }
 }
 
+/**
+ * Make an API client using the given API root and fetch client.
+ */
 export function makeClient(root: string, f = fetch): ApiClient {
   let pending: Promise<ImageResponse> | undefined;
 
@@ -388,6 +499,12 @@ export function makeClient(root: string, f = fetch): ApiClient {
   };
 }
 
+/**
+ * Parse a successful API response into the full image response record.
+ *
+ * The server sends over the output key, and the client is in the best position to turn
+ * that into a full URL, since it already knows the root URL of the server.
+ */
 export async function parseApiResponse(root: string, res: Response): Promise<ImageResponse> {
   type LimitedResponse = Omit<ImageResponse, 'output'> & { output: string };
 
diff --git a/gui/src/config.ts b/gui/src/config.ts
index e03cc77a..0442deb1 100644
--- a/gui/src/config.ts
+++ b/gui/src/config.ts
@@ -14,23 +14,40 @@ export interface ConfigString {
   keys: Array<string>;
 }
 
+/**
+ * Helper type to filter keys whose value extends `TValid`.
+ */
 export type KeyFilter<T extends object, TValid = number | string> = {
   [K in keyof T]: T[K] extends TValid ? K : never;
 }[keyof T];
 
+/**
+ * Keep fields with a file-like value, but make them optional.
+ */
 export type ConfigFiles<T extends object> = {
   [K in KeyFilter<T, Blob | File>]: Maybe<T[K]>;
 };
 
+/**
+ * Map numbers and strings to their corresponding config types and drop the rest of the fields.
+ */
 export type ConfigRanges<T extends object> = {
   [K in KeyFilter<T>]: T[K] extends number ? ConfigNumber : T[K] extends string ? ConfigString : never;
 };
 
+/**
+ * Keep fields whose value extends `TValid` and drop the rest.
+ */
 export type ConfigState<T extends object, TValid = number | string> = {
   [K in KeyFilter<T, TValid>]: T[K] extends TValid ? T[K] : never;
 };
 
+// eslint does not understand how to indent this and expects each line to increase
 /* eslint-disable */
+/**
+ * Combine all of the request parameter groups, make optional parameters required, then
+ * map them to the number/string ranges.
+ */
 export type ServerParams = ConfigRanges<Required<
   Img2ImgParams &
   Txt2ImgParams &
@@ -43,6 +60,9 @@ export type ServerParams = ConfigRanges<Required<
 };
 /* eslint-enable */
 
+/**
+ * Parameters that can be customized on the client, through the config file or settings tab.
+ */
 export interface ClientParams {
   model: ConfigString;
   platform: ConfigString;
@@ -57,11 +77,6 @@ export interface Config<T = ClientParams> {
   params: T;
 }
 
-export const DEFAULT_BRUSH = {
-  color: 255,
-  size: 8,
-};
-
 export const IMAGE_FILTER = '.bmp, .jpg, .jpeg, .png';
 export const PARAM_VERSION = '>=0.4.0';
 
diff --git a/gui/src/state.ts b/gui/src/state.ts
index 3ef7be19..4389d9bd 100644
--- a/gui/src/state.ts
+++ b/gui/src/state.ts
@@ -12,15 +12,47 @@ import {
   InpaintParams,
   ModelParams,
   OutpaintPixels,
-  paramsFromConfig,
   Txt2ImgParams,
   UpscaleParams,
   UpscaleReqParams,
 } from './client.js';
 import { Config, ConfigFiles, ConfigState, ServerParams } from './config.js';
 
+/**
+ * Combine optional files and required ranges.
+ */
 type TabState<TabParams> = ConfigFiles<Required<TabParams>> & ConfigState<Required<TabParams>>;
 
+interface BrushSlice {
+  brush: BrushParams;
+
+  setBrush(brush: Partial<BrushParams>): void;
+}
+
+interface DefaultSlice {
+  defaults: TabState<BaseImgParams>;
+
+  setDefaults(param: Partial<BaseImgParams>): void;
+}
+
+interface HistorySlice {
+  history: Array<ImageResponse>;
+  limit: number;
+  loading: Maybe<ImageResponse>;
+
+  pushHistory(image: ImageResponse): void;
+  removeHistory(image: ImageResponse): void;
+  setLimit(limit: number): void;
+  setLoading(image: Maybe<ImageResponse>): void;
+}
+
+interface ModelSlice {
+  model: ModelParams;
+
+  setModel(model: Partial<ModelParams>): void;
+}
+
+// #region tab slices
 interface Txt2ImgSlice {
   txt2img: TabState<Txt2ImgParams>;
 
@@ -42,35 +74,12 @@ interface InpaintSlice {
   resetInpaint(): void;
 }
 
-interface HistorySlice {
-  history: Array<ImageResponse>;
-  limit: number;
-  loading: Maybe<ImageResponse>;
-
-  pushHistory(image: ImageResponse): void;
-  removeHistory(image: ImageResponse): void;
-  setLimit(limit: number): void;
-  setLoading(image: Maybe<ImageResponse>): void;
-}
-
-interface DefaultSlice {
-  defaults: TabState<BaseImgParams>;
-
-  setDefaults(param: Partial<BaseImgParams>): void;
-}
-
 interface OutpaintSlice {
   outpaint: OutpaintPixels;
 
   setOutpaint(pixels: Partial<OutpaintPixels>): void;
 }
 
-interface BrushSlice {
-  brush: BrushParams;
-
-  setBrush(brush: Partial<BrushParams>): void;
-}
-
 interface UpscaleSlice {
   upscale: UpscaleParams;
   upscaleTab: TabState<UpscaleReqParams>;
@@ -79,13 +88,11 @@ interface UpscaleSlice {
   setUpscaleTab(params: Partial<UpscaleReqParams>): void;
   resetUpscaleTab(): void;
 }
+// #endregion
 
-interface ModelSlice {
-  model: ModelParams;
-
-  setModel(model: Partial<ModelParams>): void;
-}
-
+/**
+ * Full merged state including all slices.
+ */
 export type OnnxState
   = BrushSlice
   & DefaultSlice
@@ -97,14 +104,85 @@ export type OnnxState
   & Txt2ImgSlice
   & UpscaleSlice;
 
-export function createStateSlices(base: ServerParams) {
-  const defaults = paramsFromConfig(base);
+/**
+ * Shorthand for state creator to reduce repeated arguments.
+ */
+export type Slice<T> = StateCreator<OnnxState, [], [], T>;
 
-  const createTxt2ImgSlice: StateCreator<OnnxState, [], [], Txt2ImgSlice> = (set) => ({
+/**
+ * React context binding for API client.
+ */
+export const ClientContext = createContext<Maybe<ApiClient>>(undefined);
+
+/**
+ * React context binding for merged config, including server parameters.
+ */
+export const ConfigContext = createContext<Maybe<Config<ServerParams>>>(undefined);
+
+/**
+ * React context binding for zustand state store.
+ */
+export const StateContext = createContext<Maybe<StoreApi<OnnxState>>>(undefined);
+
+/**
+ * Current state version for zustand persistence.
+ */
+export const STATE_VERSION = 4;
+
+/**
+ * Default parameters for the inpaint brush.
+ *
+ * Not provided by the server yet.
+ */
+export const DEFAULT_BRUSH = {
+  color: 255,
+  size: 8,
+  strength: 0.5,
+};
+
+/**
+ * Default parameters for the image history.
+ *
+ * Not provided by the server yet.
+ */
+export const DEFAULT_HISTORY = {
+  /**
+   * The number of images to be shown.
+   */
+  limit: 4,
+
+  /**
+   * The number of additional images to be kept in history, so they can scroll
+   * back into view when you delete one. Does not include deleted images.
+   */
+  scrollback: 2,
+};
+
+export function baseParamsFromServer(defaults: ServerParams): Required<BaseImgParams> {
+  return {
+    cfg: defaults.cfg.default,
+    negativePrompt: defaults.negativePrompt.default,
+    prompt: defaults.prompt.default,
+    scheduler: defaults.scheduler.default,
+    steps: defaults.steps.default,
+    seed: defaults.seed.default,
+  };
+}
+
+/**
+ * Prepare the state slice constructors.
+ *
+ * In the default state, image sources should be null and booleans should be false. Everything
+ * else should be initialized from the default value in the base parameters.
+ */
+export function createStateSlices(server: ServerParams) {
+  const base = baseParamsFromServer(server);
+
+  const createTxt2ImgSlice: Slice<Txt2ImgSlice> = (set) => ({
     txt2img: {
-      ...defaults,
-      width: base.width.default,
-      height: base.height.default,
+      ...base,
+      width: server.width.default,
+      height: server.height.default,
     },
     setTxt2Img(params) {
       set((prev) => ({
@@ -117,19 +195,19 @@ export function createStateSlices(base: ServerParams) {
     resetTxt2Img() {
       set({
         txt2img: {
-          ...defaults,
-          width: base.width.default,
-          height: base.height.default,
+          ...base,
+          width: server.width.default,
+          height: server.height.default,
         },
       });
     },
   });
 
-  const createImg2ImgSlice: StateCreator<OnnxState, [], [], Img2ImgSlice> = (set) => ({
+  const createImg2ImgSlice: Slice<Img2ImgSlice> = (set) => ({
     img2img: {
-      ...defaults,
+      ...base,
       source: null,
-      strength: base.strength.default,
+      strength: server.strength.default,
     },
     setImg2Img(params) {
       set((prev) => ({
@@ -142,23 +220,23 @@ export function createStateSlices(base: ServerParams) {
     resetImg2Img() {
       set({
         img2img: {
-          ...defaults,
+          ...base,
           source: null,
-          strength: base.strength.default,
+          strength: server.strength.default,
         },
       });
     },
   });
 
-  const createInpaintSlice: StateCreator<OnnxState, [], [], InpaintSlice> = (set) => ({
+  const createInpaintSlice: Slice<InpaintSlice> = (set) => ({
     inpaint: {
-      ...defaults,
-      fillColor: '#000000',
-      filter: 'none',
+      ...base,
+      fillColor: server.fillColor.default,
+      filter: server.filter.default,
       mask: null,
-      noise: 'histogram',
+      noise: server.noise.default,
       source: null,
-      strength: 1.0,
+      strength: server.strength.default,
     },
     setInpaint(params) {
       set((prev) => ({
@@ -171,21 +249,21 @@ export function createStateSlices(base: ServerParams) {
     resetInpaint() {
       set({
         inpaint: {
-          ...defaults,
-          fillColor: '#000000',
-          filter: 'none',
+          ...base,
+          fillColor: server.fillColor.default,
+          filter: server.filter.default,
           mask: null,
-          noise: 'histogram',
+          noise: server.noise.default,
           source: null,
-          strength: 1.0,
+          strength: server.strength.default,
         },
       });
     },
   });
 
-  const createHistorySlice: StateCreator<OnnxState, [], [], HistorySlice> = (set) => ({
+  const createHistorySlice: Slice<HistorySlice> = (set) => ({
     history: [],
-    limit: 4,
+    limit: DEFAULT_HISTORY.limit,
     loading: null,
     pushHistory(image) {
       set((prev) => ({
@@ -193,7 +271,7 @@ export function createStateSlices(base: ServerParams) {
         history: [
           image,
           ...prev.history,
-        ].slice(0, prev.limit),
+        ].slice(0, prev.limit + DEFAULT_HISTORY.scrollback),
         loading: null,
       }));
     },
@@ -217,13 +295,13 @@ export function createStateSlices(base: ServerParams) {
     },
   });
 
-  const createOutpaintSlice: StateCreator<OnnxState, [], [], OutpaintSlice> = (set) => ({
+  const createOutpaintSlice: Slice<OutpaintSlice> = (set) => ({
     outpaint: {
       enabled: false,
-      left: 0,
-      right: 0,
-      top: 0,
-      bottom: 0,
+      left: server.left.default,
+      right: server.right.default,
+      top: server.top.default,
+      bottom: server.bottom.default,
     },
     setOutpaint(pixels) {
       set((prev) => ({
@@ -235,11 +313,9 @@ export function createStateSlices(base: ServerParams) {
     },
   });
 
-  const createBrushSlice: StateCreator<OnnxState, [], [], BrushSlice> = (set) => ({
+  const createBrushSlice: Slice<BrushSlice> = (set) => ({
     brush: {
-      color: 255,
-      size: 8,
-      strength: 0.5,
+      ...DEFAULT_BRUSH,
     },
     setBrush(brush) {
       set((prev) => ({
@@ -251,14 +327,14 @@ export function createStateSlices(base: ServerParams) {
     },
   });
 
-  const createUpscaleSlice: StateCreator<OnnxState, [], [], UpscaleSlice> = (set) => ({
+  const createUpscaleSlice: Slice<UpscaleSlice> = (set) => ({
     upscale: {
-      denoise: 0.5,
+      denoise: server.denoise.default,
       enabled: false,
       faces: false,
-      scale: 1,
-      outscale: 1,
-      faceStrength: 0.5,
+      scale: server.scale.default,
+      outscale: server.outscale.default,
+      faceStrength: server.faceStrength.default,
     },
     upscaleTab: {
       source: null,
@@ -288,9 +364,9 @@ export function createStateSlices(base: ServerParams) {
     },
   });
 
-  const createDefaultSlice: StateCreator<OnnxState, [], [], DefaultSlice> = (set) => ({
+  const createDefaultSlice: Slice<DefaultSlice> = (set) => ({
     defaults: {
-      ...defaults,
+      ...base,
     },
     setDefaults(params) {
       set((prev) => ({
@@ -302,12 +378,12 @@ export function createStateSlices(base: ServerParams) {
     },
   });
 
-  const createModelSlice: StateCreator<OnnxState, [], [], ModelSlice> = (set) => ({
+  const createModelSlice: Slice<ModelSlice> = (set) => ({
     model: {
-      model: '',
-      platform: '',
-      upscaling: '',
-      correction: '',
+      model: server.model.default,
+      platform: server.platform.default,
+      upscaling: server.upscaling.default,
+      correction: server.correction.default,
     },
     setModel(params) {
       set((prev) => ({
@@ -331,8 +407,3 @@ export function createStateSlices(base: ServerParams) {
     createUpscaleSlice,
   };
 }
-
-export const ClientContext = createContext<Maybe<ApiClient>>(undefined);
-export const ConfigContext = createContext<Maybe<Config<ServerParams>>>(undefined);
-export const StateContext = createContext<Maybe<StoreApi<OnnxState>>>(undefined);
-export const STATE_VERSION = 4;