diff --git a/AGENTS.md b/AGENTS.md
index 4a9ae95..257b466 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -18,7 +18,7 @@
 |---|---|---|
 | 框架 | Astro | ^5.18.1 |
 | UI 组件 | Svelte | ^5.55.2 |
-| 编辑器 | CodeMirror 6 | codemirror ^6.0.2 |
+| 编辑器 | CodeMirror 6 | codemirror ^6.0.2, @codemirror/autocomplete ^6.20.3 |
 | 样式 | Tailwind CSS v4 + DaisyUI v5 | @tailwindcss/vite ^4.2.2, daisyui ^5.5.19 |
 | 语言 | TypeScript | ^5.9.3 |
 | 高精度数值 | decimal.js | ^10.6.0 |
@@ -56,6 +56,7 @@ calcuko/
     │   ├── language/                 # 表达式语言 tokenizer、AST、Pratt parser、源码位置类型及测试
     │   ├── types.ts                  # 共享类型定义（LineResult）
     │   ├── constants.ts              # 示例公式和帮助弹窗元数据
+    │   ├── autocomplete.ts           # CodeMirror 智能补全候选与 Tab 接受逻辑
     │   ├── evaluator.ts              # ⭐ 内置注册、逐行求值和统一 formatter
     │   ├── resultFormatting.ts        # 行级结果格式选项、精度与显示转换
     │   ├── editorExtensions.ts         # CodeMirror 高亮、错误/hover 行与高度 spacer
@@ -112,6 +113,7 @@ calcuko/
 - **数值模型**：整数为任意精度 BigInt，小数使用 34 位有效数字且 half-even 舍入的 Decimal，`a$b` 为自动约分的精确 Rational；混合运算按 BigInt → Rational → Decimal 提升
 - **语法高亮**：`src/lib/highlight.ts` 与 CodeMirror 装饰层直接消费求值语言 tokenizer 的 token，支持注释、字符串、数值（含 SI 与进制）、运算符（含逗号等标点）、括号和变量，并以不同颜色区分内置函数与自定义函数；高亮模式按行恢复词法错误，以错误样式显示未知字符和未闭合字符串并继续着色，求值模式仍严格报错
 - **括号匹配**：光标定位时高亮配对括号 `()[]{}`
+- **智能补全**：输入标识符时以浮动框提示当前行上方已进入作用域的变量、自定义函数及全部内置函数；内置函数候选显示签名与简要功能说明，Tab 仅在补全激活时接受候选
 - **帮助弹窗**：Header 中的「帮助」按钮展示基本语法、函数和常量元数据，支持 Escape 关闭、关闭按钮标签及打开/关闭焦点恢复
 - **编辑器标题栏操作**：载入示例和清空均先确认、写入同一持久化 key，并提供单步撤销
 - **变量快照复制**：变量快照以 button 形式展示 `name = value`，点击通过 `navigator.clipboard.writeText()` 复制值，并显示 2 秒自动消失的「已复制」Toast
@@ -137,6 +139,7 @@ calcuko/
   - 内置函数 `#a78bfa`（淡紫）、自定义函数 `#22d3ee`（青色）
 - **编辑器选区**：文本选中背景使用半透明主题主色（玫瑰粉），保持高亮叠层文字可见
 - **错误行标识**：编辑器以半透明错误色背景和左侧红色边线标记求值失败的整行，未知字符使用红色波浪下划线显示
+- **智能补全浮层**：使用主题 base-200 背景、base-300 边框与圆角阴影，列表与浮层四边保持等量内边距；选中项使用半透明主色，函数和变量图标分别沿用函数紫与变量蓝
 - **Tailwind v4 语法**：使用 `@import "tailwindcss"` 和 `@plugin "daisyui"` 而非旧版 `@tailwind` 指令
 - **字体大小**：在 `@theme` 块中自定义了 `--text-xs` 到 `--text-6xl`
 
diff --git a/e2e/calculator.spec.ts b/e2e/calculator.spec.ts
index 711d323..d063d50 100644
--- a/e2e/calculator.spec.ts
+++ b/e2e/calculator.spec.ts
@@ -40,6 +40,29 @@ test("shows a visible themed editor cursor", async ({ page }) => {
 	await expect(cursor).toHaveCSS("border-left-color", "rgb(251, 113, 133)");
 });
 
+test("autocompletes earlier symbols and built-ins with Tab without consuming a normal Tab", async ({ page }) => {
+	await page.goto("./");
+	await setSource(page, "total = 42\nfn triple(value)=value*3\ntot");
+	await expect(page.locator(".cm-tooltip-autocomplete")).toBeVisible();
+	await expect(page.locator(".cm-completionLabel", { hasText: "total" })).toBeVisible();
+	await expect(page.locator(".cm-tooltip-autocomplete")).toHaveCSS("border-top-width", "1px");
+	await expect(page.locator(".cm-tooltip-autocomplete")).toHaveCSS("border-radius", "16px");
+	const variableIconColor = await page.locator(".cm-completionIcon-variable").first().evaluate((icon) => getComputedStyle(icon, "::after").color);
+	await expect(page.locator(".cm-tooltip-autocomplete")).toHaveCSS("padding", "8px");
+	expect(variableIconColor).toBe("rgb(14, 165, 233)");
+	await editor(page).press("Tab");
+	await expect(page.locator(".cm-line").nth(2)).toHaveText("total");
+
+	await editor(page).press("Enter");
+	await editor(page).pressSequentially("sq");
+	await expect(page.locator(".cm-completionLabel", { hasText: "sqrt" })).toBeVisible();
+	await expect(page.locator(".cm-completionLabel", { hasText: "sqrt" }).locator("..").locator(".cm-completionDetail")).toContainText("平方根");
+	await editor(page).press("Escape");
+	const before = await editor(page).textContent();
+	await editor(page).press("Tab");
+	await expect(editor(page)).toHaveText(before ?? "");
+});
+
 test("shows matrices, errors, and color previews", async ({ page }) => {
 	await page.goto("./");
 	await setSource(page, "missing\nmatrix([[1,2],[3,4]])\nrgb(255,0,0)");
diff --git a/package-lock.json b/package-lock.json
index 03ba77e..ed80395 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -9,6 +9,7 @@
       "version": "1.1.0",
       "dependencies": {
         "@astrojs/svelte": "^7.2.5",
+        "@codemirror/autocomplete": "^6.20.3",
         "@codemirror/state": "^6.7.1",
         "@codemirror/view": "^6.43.9",
         "@tailwindcss/vite": "^4.2.2",
diff --git a/package.json b/package.json
index 9ece7e3..13e121c 100644
--- a/package.json
+++ b/package.json
@@ -14,6 +14,7 @@
   },
   "dependencies": {
     "@astrojs/svelte": "^7.2.5",
+    "@codemirror/autocomplete": "^6.20.3",
     "@codemirror/state": "^6.7.1",
     "@codemirror/view": "^6.43.9",
     "@tailwindcss/vite": "^4.2.2",
diff --git a/src/components/FormulaCalculator.svelte b/src/components/FormulaCalculator.svelte
index 7fb1598..e77a0a1 100644
--- a/src/components/FormulaCalculator.svelte
+++ b/src/components/FormulaCalculator.svelte
@@ -10,6 +10,7 @@
 	import { isMatrix } from "../lib/language/matrix";
 	import { formatOptions, formatResult, type FormatOption, type ResultFormat, type ResultValueKind } from "../lib/resultFormatting";
 	import { editorUiField, setEditorUi, syntaxDecorations } from "../lib/editorExtensions";
+	import { calcukoAutocomplete } from "../lib/autocomplete";
 
 	const BASE_URL = import.meta.env.BASE_URL.replace(/\/?$/, "");
 	const APP_VERSION = import.meta.env.PUBLIC_APP_VERSION?.trim() || "dev";
@@ -116,7 +117,7 @@
 		} catch { localStorage.removeItem(formatStorageKey); }
 		editorView = new EditorView({
 			parent: editorHost,
-			state: EditorState.create({ doc: source, extensions: [basicSetup, editorUiField, syntaxDecorations, EditorView.theme({ "&": { height: "100%" }, ".cm-scroller": { overflow: "auto", fontFamily: "ui-monospace, SFMono-Regular, Menlo, monospace" }, ".cm-line": { minHeight: "24px", lineHeight: "24px", padding: "0 16px" }, ".cm-content": { padding: "16px 0" }, ".cm-gutters": { backgroundColor: "color-mix(in oklab, var(--color-base-200) 40%, transparent)", borderRight: "1px solid var(--color-base-300)" }, ".cm-activeLine": { backgroundColor: "color-mix(in oklab, var(--color-primary) 10%, transparent)" }, ".cm-activeLineGutter": { backgroundColor: "color-mix(in oklab, var(--color-primary) 12%, transparent)" }, ".cm-result-hover-line": { backgroundColor: "color-mix(in oklab, var(--color-primary) 22%, transparent) !important", boxShadow: "inset 3px 0 var(--color-primary)" }, ".cm-error-line": { backgroundColor: "color-mix(in oklab, var(--color-error) 18%, transparent)", boxShadow: "inset 3px 0 var(--color-error)" } }) , EditorView.updateListener.of((update) => {
+			state: EditorState.create({ doc: source, extensions: [basicSetup, calcukoAutocomplete, editorUiField, syntaxDecorations, EditorView.theme({ "&": { height: "100%" }, ".cm-scroller": { overflow: "auto", fontFamily: "ui-monospace, SFMono-Regular, Menlo, monospace" }, ".cm-line": { minHeight: "24px", lineHeight: "24px", padding: "0 16px" }, ".cm-content": { padding: "16px 0" }, ".cm-gutters": { backgroundColor: "color-mix(in oklab, var(--color-base-200) 40%, transparent)", borderRight: "1px solid var(--color-base-300)" }, ".cm-activeLine": { backgroundColor: "color-mix(in oklab, var(--color-primary) 10%, transparent)" }, ".cm-activeLineGutter": { backgroundColor: "color-mix(in oklab, var(--color-primary) 12%, transparent)" }, ".cm-result-hover-line": { backgroundColor: "color-mix(in oklab, var(--color-primary) 22%, transparent) !important", boxShadow: "inset 3px 0 var(--color-primary)" }, ".cm-error-line": { backgroundColor: "color-mix(in oklab, var(--color-error) 18%, transparent)", boxShadow: "inset 3px 0 var(--color-error)" } }) , EditorView.updateListener.of((update) => {
 				if (update.docChanged) { const next = update.state.doc.toString(); reconcileFormats(source, next); source = next; localStorage.setItem(storageKey, source); persistFormats(); }
 				if (update.docChanged || update.selectionSet) activeLine = update.state.doc.lineAt(update.state.selection.main.head).number;
 				if (update.selectionSet) queueMicrotask(dispatchEditorUi);
@@ -421,6 +422,15 @@
 	:global(.cm-line-spacer-active) { background: color-mix(in oklab, var(--color-primary) 10%, transparent); }
 	:global(.cm-line-spacer-hover) { background: color-mix(in oklab, var(--color-primary) 22%, transparent); box-shadow: inset 3px 0 var(--color-primary); }
 	:global(.cm-line-spacer-error) { background: color-mix(in oklab, var(--color-error) 18%, transparent); box-shadow: inset 3px 0 var(--color-error); }
+	:global(.cm-tooltip.cm-tooltip-autocomplete) { box-sizing: border-box; padding: 0.5rem; background: var(--color-base-200); color: var(--color-base-content); border: 1px solid var(--color-base-300); border-radius: var(--radius-box); box-shadow: 0 16px 40px rgb(0 0 0 / 0.45), 0 0 0 1px color-mix(in oklab, var(--color-primary) 8%, transparent); overflow: hidden; }
+	:global(.cm-tooltip-autocomplete > ul) { box-sizing: border-box; min-width: 15rem; max-height: 15rem; height: auto; padding: 0; font-family: ui-monospace, SFMono-Regular, Menlo, monospace; }
+	:global(.cm-tooltip-autocomplete > ul > li) { min-height: 2rem; padding: 0.3rem 0.625rem; border-radius: calc(var(--radius-field) / 2); color: color-mix(in oklab, var(--color-base-content) 82%, transparent); }
+	:global(.cm-tooltip-autocomplete > ul > li[aria-selected]) { background: color-mix(in oklab, var(--color-primary) 22%, var(--color-base-200)) !important; color: var(--color-base-content) !important; }
+	:global(.cm-completionLabel) { font-weight: 600; }
+	:global(.cm-completionMatchedText) { color: var(--color-primary); font-weight: 800; text-decoration: none; }
+	:global(.cm-completionDetail) { color: color-mix(in oklab, var(--color-base-content) 48%, transparent); font-style: normal; margin-left: 1rem; }
+	:global(.cm-completionIcon-function::after) { color: #a78bfa; }
+	:global(.cm-completionIcon-variable::after) { color: #0ea5e9; }
 
 	div::-webkit-scrollbar {
 		display: none;
diff --git a/src/lib/autocomplete.test.ts b/src/lib/autocomplete.test.ts
new file mode 100644
index 0000000..9096f6f
--- /dev/null
+++ b/src/lib/autocomplete.test.ts
@@ -0,0 +1,31 @@
+import { describe, expect, it } from "vitest";
+import { completionOptions } from "./autocomplete";
+
+describe("completionOptions", () => {
+	it("includes earlier variables, custom functions, and built-in functions", () => {
+		const source = "金额 = 12\nfn double(value)=value*2\ndou";
+		const options = completionOptions(source, source.length);
+
+		expect(options).toEqual(expect.arrayContaining([
+			expect.objectContaining({ label: "金额", type: "variable", detail: "上方变量" }),
+			expect.objectContaining({ label: "double", type: "function", detail: "自定义函数 (value)" }),
+			expect.objectContaining({ label: "sqrt", type: "function", detail: "Math.sqrt(x) — 平方根" }),
+		]));
+	});
+
+	it("does not suggest declarations from the current or following lines", () => {
+		const source = "first = 1\ncurrent = fir\nlater = 3";
+		const labels = completionOptions(source, source.indexOf("fir", source.indexOf("current")) + 3).map(({ label }) => label);
+
+		expect(labels).toContain("first");
+		expect(labels).not.toContain("current");
+		expect(labels).not.toContain("later");
+	});
+
+	it("keeps a shadowing user function instead of its built-in namesake", () => {
+		const source = "fn sqrt(value)=value\nsq";
+		const sqrt = completionOptions(source, source.length).find(({ label }) => label === "sqrt");
+
+		expect(sqrt).toMatchObject({ detail: "自定义函数 (value)", boost: 2 });
+	});
+});
diff --git a/src/lib/autocomplete.ts b/src/lib/autocomplete.ts
new file mode 100644
index 0000000..b11debe
--- /dev/null
+++ b/src/lib/autocomplete.ts
@@ -0,0 +1,55 @@
+import { acceptCompletion, autocompletion, type Completion, type CompletionContext, type CompletionResult } from "@codemirror/autocomplete";
+import { Prec } from "@codemirror/state";
+import { keymap } from "@codemirror/view";
+import { mathContext } from "./evaluator";
+import { mathFunctions } from "./constants";
+import { parse } from "./language/parser";
+
+const identifierBeforeCursor = /(?:[\p{ID_Start}$]|\p{Extended_Pictographic})(?:[\p{ID_Continue}$]|\p{Extended_Pictographic})*$/u;
+
+const builtinCompletions: Completion[] = Object.entries(mathContext)
+	.filter(([, value]) => typeof value === "function")
+	.map(([label]) => ({ label, type: "function", detail: mathFunctions[label] ?? "内置函数", boost: 0 }))
+	.sort((left, right) => left.label.localeCompare(right.label));
+
+export function completionOptions(source: string, cursor: number): Completion[] {
+	const lineStart = source.lastIndexOf("\n", Math.max(0, cursor - 1)) + 1;
+	const options = new Map<string, Completion>();
+
+	for (const line of source.slice(0, lineStart).split("\n")) {
+		try {
+			const statement = parse(line);
+			if (statement.kind === "functionDefinition") {
+				options.set(statement.name, { label: statement.name, type: "function", detail: `自定义函数 (${statement.parameters.join(", ")})`, boost: 2 });
+			} else if (statement.kind === "assignment") {
+				const parameters = statement.value.kind === "lambda" ? statement.value.parameters : undefined;
+				options.set(statement.name, parameters
+					? { label: statement.name, type: "function", detail: `自定义函数 (${parameters.join(", ")})`, boost: 2 }
+					: { label: statement.name, type: "variable", detail: "上方变量", boost: 1 });
+			} else if (statement.kind === "destructuringAssignment") {
+				for (const label of statement.names) options.set(label, { label, type: "variable", detail: "上方变量", boost: 1 });
+			}
+		} catch {
+			// 正在编辑或语法错误的行不会向后方作用域贡献候选。
+		}
+	}
+	for (const option of builtinCompletions) {
+		if (!options.has(option.label)) options.set(option.label, option);
+	}
+	return [...options.values()];
+}
+
+export function calcukoCompletionSource(context: CompletionContext): CompletionResult | null {
+	const word = context.matchBefore(identifierBeforeCursor);
+	if (!word && !context.explicit) return null;
+	return {
+		from: word?.from ?? context.pos,
+		options: completionOptions(context.state.doc.toString(), context.pos),
+		validFor: identifierBeforeCursor,
+	};
+}
+
+export const calcukoAutocomplete = [
+	autocompletion({ override: [calcukoCompletionSource], activateOnTyping: true }),
+	Prec.highest(keymap.of([{ key: "Tab", run: acceptCompletion }])),
+];
diff --git a/src/lib/constants.ts b/src/lib/constants.ts
index 9389c7f..1d279e5 100644
--- a/src/lib/constants.ts
+++ b/src/lib/constants.ts
@@ -24,12 +24,27 @@ export const mathFunctions: Record<string, string> = {
 	decimal: "decimal(x) — 转 34 位高精度小数",
 	rat: "rat(a, b) — 构造精确分数 a$b",
 	range: "range(start, stop, step?) — 生成不含终点的数值范围",
+	len: "len(array) — 获取数组长度",
+	reverse: "reverse(array) — 反转数组顺序",
 	sum: "sum(array) — 数组求和",
 	ave: "ave(array) — 数组平均值",
+	minArray: "minArray(array) — 获取数组最小值",
+	maxArray: "maxArray(array) — 获取数组最大值",
 	map: "map(array, fn) — 映射数组",
+	aggregate: "aggregate(array, fn) — 逐项归并数组",
 	filter: "filter(array, fn) — 过滤数组",
 	sort: "sort(array, fn?) — 排序数组",
 	unique: "unique(array) — 数组去重",
+	count1: "count1(width, value) — 统计置位比特数",
+	rotateL: "rotateL(width, value, n?) — 循环左移",
+	rotateR: "rotateR(width, value, n?) — 循环右移",
+	reverseBits: "reverseBits(width, value) — 翻转比特顺序",
+	reverseBytes: "reverseBytes(width, value) — 翻转字节顺序",
+	swapNib: "swapNib(width, value) — 交换半字节",
+	evenParity: "evenParity(width, value) — 计算偶校验位",
+	oddParity: "oddParity(width, value) — 计算奇校验位",
+	pack: "pack(bytes, values) — 将整数数组打包",
+	unpack: "unpack(bytes, count, value) — 将整数拆分为数组",
 	matrix: "matrix(rows) — 从二维数组构造矩阵",
 	row: "row(values...) — 构造单行矩阵",
 	col: "col(values...) — 构造单列矩阵",