diff --git a/analyzer-views/README.md b/analyzer-views/README.md
index a18163d..5572573 100644
--- a/analyzer-views/README.md
+++ b/analyzer-views/README.md
@@ -22,7 +22,8 @@ sequence.sequence = analyzerSeqText;         // the text of spec/analyzer.seq
 sequence.addEventListener("nlp-open", (e) => openFile(e.detail.path));
 
 const kb = document.createElement("nlp-knowledge-base");
-kb.files = [{ path: "kb/user/colors.dict", bytes: 3000 }];   // sizes are optional
+kb.files = [{ path: "kb/user/colors.dict", bytes: 3000,       // sizes are optional,
+	description: kbDescription(colorsDictText) }];             // and so is the mouse-over
 kb.addEventListener("nlp-open", (e) => openFile(e.detail.path));
 
 sidebar.append(sequence, kb);
@@ -42,7 +43,7 @@ Every list element takes:
 
 | | |
 |---|---|
-| `files` (property) | The paths to list: strings, or `{ path, bytes }` objects to show sizes. `<nlp-trees>` takes `trees` instead. |
+| `files` (property) | The paths to list: strings, or `{ path, bytes }` objects to show sizes. On `<nlp-knowledge-base>`, a `description` too: the file's mouse-over, above its path. `<nlp-trees>` takes `trees` instead. |
 | `selected` (property) | The path that's open now, drawn as selected. |
 | `changed` (property) | Paths with unsaved edits. Each gets a mark, plus a revert button when the element has `revertable`. |
 | `heading` (attribute) | The list's heading. `heading=""` shows no heading. |
@@ -144,7 +145,11 @@ follow the same light and dark choice.
 
 - `passes(seqText, files)` reads `analyzer.seq` into passes, numbered the way the engine
   numbers them. A switched-off pass keeps its number, and a folder or stub gets none.
-- `shownInKnowledgeBase(path)` says whether a file is listed in the knowledge base.
+- `shownInKnowledgeBase(path)` says whether a file is listed in the knowledge base, and
+  `kbLabel(path)` names it there: its path under `kb/user/`.
+- `kbDescription(text)` is what a `.dict` or `.kbb` file holds, from the comment
+  paragraph at its top, as the extension's knowledge base view shows on mouse-over. Only
+  the first 4 KB are read, so a head of the file is enough.
 - `passTooltip`, `passLabel`, `passIcon`, `fileIcon` and `fileSize` give each row's
   mouse-over, label, icon and size.
 - `outputOrder`, `treeOrder`, `treeLabel`, `treeTitle` and `treeNote` order and describe
diff --git a/analyzer-views/package-lock.json b/analyzer-views/package-lock.json
index 6b877b9..5db7d97 100644
--- a/analyzer-views/package-lock.json
+++ b/analyzer-views/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "@visualtext/analyzer-views",
-  "version": "0.3.0",
+  "version": "0.6.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "@visualtext/analyzer-views",
-      "version": "0.3.0",
+      "version": "0.6.0",
       "dependencies": {
         "@shikijs/core": "4.4.3",
         "@shikijs/engine-javascript": "4.4.3",
diff --git a/analyzer-views/package.json b/analyzer-views/package.json
index 1d19b79..bc1d82a 100644
--- a/analyzer-views/package.json
+++ b/analyzer-views/package.json
@@ -1,7 +1,7 @@
 {
   "name": "@visualtext/analyzer-views",
   "private": true,
-  "version": "0.5.0",
+  "version": "0.6.0",
   "description": "An NLP++ analyzer's sequence, knowledge base, run results, values, code and log, shown the way the NLP++ extension for VS Code shows them, for any web page.",
   "type": "module",
   "repository": {
diff --git a/analyzer-views/src/elements.ts b/analyzer-views/src/elements.ts
index 3659f79..c604d71 100644
--- a/analyzer-views/src/elements.ts
+++ b/analyzer-views/src/elements.ts
@@ -16,7 +16,9 @@
 //   seq.sequence = seqText;
 //   seq.addEventListener("nlp-open", (e) => open(e.detail.path));
 //
-// Properties:  files      paths, or { path, bytes } to show sizes (all but <nlp-trees>)
+// Properties:  files      paths, or { path, bytes } to show sizes (all but <nlp-trees>);
+//                         on <nlp-knowledge-base>, { description } too, the mouse-over
+//                         (kbDescription of the file's text)
 //              sequence   the text of spec/analyzer.seq (<nlp-sequence>)
 //              trees      { name, pass, passName, bytes } and skipped, names too large
 //                         to keep (<nlp-trees>); on <nlp-sequence>, the trees a -DEV run
@@ -39,7 +41,7 @@
 // LIGHT DOM, not a shadow root: the rows are ordinary buttons a page can style, test and
 // query (button[data-path]). style.css draws them; its --nlp-* properties theme them.
 
-import { type AnalyzerFile, fileSize, shownInKnowledgeBase, toFile } from "./files.js";
+import { type AnalyzerFile, fileSize, kbLabel, shownInKnowledgeBase, toFile } from "./files.js";
 import { nlpTokens } from "./highlight.js";
 import { type IconName, fileIcon, iconElement, passIcon } from "./icons.js";
 import { type NlpLanguage, NLP_LANGUAGES, langFor } from "./languages.js";
@@ -310,10 +312,11 @@ export class NlpKnowledgeBase extends FileList {
 
 	protected rows(): Row[] {
 		return this.files.filter((f) => shownInKnowledgeBase(f.path)).map((f) => ({
-			label: f.path.slice("kb/".length),
+			label: kbLabel(f.path),
 			path: f.path,
 			icon: fileIcon(f.path),
-			title: f.path,
+			// What the file holds, over where it lives, as the extension's mouse-over.
+			title: f.description ? `${f.description}\n\n${f.path}` : f.path,
 			size: fileSize(f.bytes),
 		}));
 	}
diff --git a/analyzer-views/src/files.ts b/analyzer-views/src/files.ts
index 66f25d6..7dc5b2c 100644
--- a/analyzer-views/src/files.ts
+++ b/analyzer-views/src/files.ts
@@ -3,10 +3,12 @@
 // PURE: no DOM.
 
 // A file of the analyzer: its path inside the analyzer (spec/..., kb/..., input/...),
-// and its size when the host knows it.
+// its size when the host knows it, and, for a knowledge-base file, what it holds
+// (kbDescription of its text) to show when the mouse is over it.
 export interface AnalyzerFile {
 	path: string;
 	bytes?: number;
+	description?: string;
 }
 
 export function toFile(file: string | AnalyzerFile): AnalyzerFile {
@@ -20,6 +22,57 @@ export function shownInKnowledgeBase(path: string): boolean {
 	return path.startsWith("kb/") && /\.(dict|kbb)$/i.test(path);
 }
 
+// A knowledge-base file's name in the list: its path under kb/user/, where an analyzer's
+// own files live -- "colors.dict" rather than "kb/user/colors.dict".
+export function kbLabel(path: string): string {
+	return path.replace(/^kb\/(user\/)?/, "");
+}
+
+// What a .dict or .kbb file holds, as its author says in the comment at the top of it: the
+// opening paragraph of '#' or /* */ comment lines, as the extension's KNOWLEDGE BASE view
+// shows it on mouse-over (kbView.ts fileDescription). A bare '#' ends the paragraph; a '/*'
+// alone on the line opening a block comment is stepped over. "" when there is none.
+//
+// Only the head is read: en-full.kbb is 10 MB, and the description is at the top.
+const DESCRIPTION_HEAD = 4096;
+const DESCRIPTION_LINES = 8;
+
+export function kbDescription(text: string | null | undefined): string {
+	const all = String(text ?? "");
+	const lines = all.slice(0, DESCRIPTION_HEAD).split(/\r?\n/);
+	if (all.length > DESCRIPTION_HEAD) lines.pop();     // cut mid-line: not whole
+	const out: string[] = [];
+	let open = false;       // inside a /* */ comment begun on an earlier line
+	for (const line of lines) {
+		if (out.length >= DESCRIPTION_LINES) break;
+		const trimmed = line.trim();
+		if (open || trimmed.startsWith("/*")) {
+			// A block-comment line counts only when nothing follows its close.
+			const close = trimmed.indexOf("*/", open ? 0 : 2);
+			if (close >= 0 && trimmed.slice(close + 2).trim()) break;
+			open = close < 0;
+		} else if (!trimmed.startsWith("#")) {
+			break;
+		}
+		const words = stripCommentMarkers(trimmed);
+		if (!words) {
+			if (!out.length) continue;      // '/*' on a line of its own opens the block
+			break;                          // a marker-only line closes the paragraph
+		}
+		out.push(words);
+	}
+	return out.join("\n");
+}
+
+// One comment line without its markers: '#', '/*', '*/', and the '*' block comments'
+// continuation lines are often drawn with.
+function stripCommentMarkers(line: string): string {
+	let text = line;
+	if (text.startsWith("/*")) text = text.slice(2);
+	if (text.endsWith("*/")) text = text.slice(0, -2);
+	return text.replace(/^[#*\s]+/, "").trim();
+}
+
 // A size for a list: "3 KB", "1.2 MB". Unknown or empty prints nothing rather than
 // claiming "0 KB".
 export function fileSize(bytes: number | null | undefined): string {
diff --git a/analyzer-views/test/elements.test.ts b/analyzer-views/test/elements.test.ts
index 792035d..5a90521 100644
--- a/analyzer-views/test/elements.test.ts
+++ b/analyzer-views/test/elements.test.ts
@@ -113,9 +113,16 @@ describe("<nlp-knowledge-base>", () => {
 		document.body.append(el);
 		expect(el.querySelector("h3")?.textContent).toBe("Knowledge base");
 		expect(paths(el)).toEqual(["kb/user/colors.dict", "kb/user/facts.kbb"]);
-		expect([...el.querySelectorAll(".nlp-name")].map((n) => n.textContent)).toEqual(["user/colors.dict", "user/facts.kbb"]);
+		expect([...el.querySelectorAll(".nlp-name")].map((n) => n.textContent)).toEqual(["colors.dict", "facts.kbb"]);
 		expect([...el.querySelectorAll(".nlp-size")].map((n) => n.textContent)).toEqual(["3 KB"]);
 	});
+	it("says on mouse-over what a file holds, over its path", () => {
+		const el = document.createElement("nlp-knowledge-base") as NlpKnowledgeBase;
+		el.files = [{ path: "kb/user/colors.dict", description: "Colour words" }, "kb/user/facts.kbb"];
+		document.body.append(el);
+		expect([...el.querySelectorAll(".nlp-name")].map((n) => n.getAttribute("title")))
+			.toEqual(["Colour words\n\nkb/user/colors.dict", "kb/user/facts.kbb"]);
+	});
 	it("hides itself when the analyzer has only .kb files", () => {
 		const el = document.createElement("nlp-knowledge-base");
 		el.files = ["kb/user/hier.kb", "kb/user/word.kb"];
diff --git a/analyzer-views/test/rules.test.ts b/analyzer-views/test/rules.test.ts
index 4fc1529..9d51936 100644
--- a/analyzer-views/test/rules.test.ts
+++ b/analyzer-views/test/rules.test.ts
@@ -2,7 +2,7 @@
 // The rules with no DOM at all, as a server or another page would use them.
 import { describe, expect, it } from "vitest";
 import {
-	fileIcon, fileSize, outputOrder, passComment, passIcon, passLabel, passTooltip, passes, shownInKnowledgeBase,
+	fileIcon, fileSize, outputOrder, passComment, passIcon, passLabel, passTooltip, passes, shownInKnowledgeBase, kbDescription, kbLabel,
 	filledFields, langFor, logLines, matchCount, matchesIn, problemWhere, problemsInLog, readOutput, ruleMatches,
 	treeLabel, treeNote, treeOrder, treeTitle,
 } from "../src/rules.js";
@@ -89,6 +89,22 @@ describe("the knowledge base", () => {
 		];
 		expect(files.filter(shownInKnowledgeBase)).toEqual(["kb/user/colors.dict", "kb/user/en-full.DICT", "kb/user/facts.kbb"]);
 	});
+	it("names a file by its path under kb/user/", () => {
+		expect(["kb/user/colors.dict", "kb/general/en.kbb", "kb/facts.kbb"].map(kbLabel)).toEqual(["colors.dict", "general/en.kbb", "facts.kbb"]);
+	});
+	it("describes a file by the comment paragraph at its top, as the extension does", () => {
+		expect(kbDescription("# Colour words\n# for the paint analyzer\n#\n# Maintained by hand\nred\tcolor=red\n"))
+			.toBe("Colour words\nfor the paint analyzer");
+		expect(kbDescription("/*\n * Facts about firms\n */\nfirm\n")).toBe("Facts about firms");
+		expect(kbDescription("/* One line */\r\nfirm\r\n")).toBe("One line");
+		expect(kbDescription("/* then */ red\n")).toBe("");
+		expect(kbDescription("red\tcolor=red\n# not at the top\n")).toBe("");
+		expect(kbDescription(undefined)).toBe("");
+	});
+	it("reads only the head of a large file", () => {
+		expect(kbDescription(`# Every English word\n${"word\n".repeat(1_000_000)}`)).toBe("Every English word");
+		expect(kbDescription(Array.from({ length: 20 }, (_, i) => `# line ${i}`).join("\n")).split("\n")).toHaveLength(8);
+	});
 	it("prints a size, and nothing for one it does not know", () => {
 		expect([fileSize(3000), fileSize(100), fileSize(2.5 * 1024 * 1024), fileSize(0), fileSize(undefined)])
 			.toEqual(["3 KB", "1 KB", "2.5 MB", "", ""]);
diff --git a/studio/src/main.ts b/studio/src/main.ts
index aeb0c2a..869c58e 100644
--- a/studio/src/main.ts
+++ b/studio/src/main.ts
@@ -22,7 +22,7 @@ import { languageFor } from "./lsp/convert";
 import { type AnalyzerEntry, fileUri, loadFiles, loadIndex, pathOf } from "./analyzers";
 import {
 	type IconName, type NlpKnowledgeBase, type NlpSequence, type Pass, type TreeFile as ListedTree,
-	fileSize, iconElement, passes, ruleMatches, treeTitle,
+	fileSize, iconElement, kbDescription, passes, ruleMatches, shownInKnowledgeBase, treeTitle,
 } from "@visualtext/analyzer-views";
 import {
 	type Account, type CommitResult, type FoundAnalyzer, type RecentAnalyzer, type RepoAnalyzers, type Repository,
@@ -887,7 +887,12 @@ export class Studio {
 		sequence.addEventListener("nlp-open-matches", (e) => void this.openMatches(e.detail.path));
 		listen(sequence);
 		const kb = document.createElement("nlp-knowledge-base");
-		kb.files = entry.files;
+		// Each file's opening comment is its mouse-over, as in the extension. Only its top
+		// lines are taken: a .kbb can run to megabytes.
+		const head = (model: monaco.editor.ITextModel | undefined) =>
+			model?.getValueInRange(new monaco.Range(1, 1, Math.min(model.getLineCount(), 20) + 1, 1));
+		kb.files = entry.files.filter(shownInKnowledgeBase)
+			.map((path) => ({ path, description: kbDescription(head(this.models.get(path))) }));
 		listen(kb);
 
 		// The studio's own lists, drawn with the same rows until they move there too.