diff --git a/dev/index.d.ts b/dev/index.d.ts
index 3e52f68..d09f0e5 100644
--- a/dev/index.d.ts
+++ b/dev/index.d.ts
@@ -1,7 +1,52 @@
-export {mathHtml, type Options as HtmlOptions} from './lib/html.js'
-export {math, type Options} from './lib/syntax.js'
+import type {KatexOptions} from 'katex'
 
+export {mathHtml} from './lib/html.js'
+export {math} from './lib/syntax.js'
+
+/**
+ * Configuration for HTML output.
+ *
+ * > 👉 **Note**: passed to `katex.renderToString`.
+ * > `displayMode` is overwritten by this plugin, to `false` for math in
+ * > text (inline), and `true` for math in flow (block).
+ */
+export interface HtmlOptions extends KatexOptions {
+  /**
+   * The field `displayMode` cannot be passed to `micromark-extension-math`.
+   * It is overwritten by it,
+   * to `false` for math in text (inline) and `true` for math in flow (block).
+   */
+  displayMode?: never
+}
+
+/**
+ * Configuration.
+ */
+export interface Options {
+  /**
+   * Whether to support math (text) with a single dollar (default: `true`).
+   *
+   * Single dollars work in Pandoc and many other places, but often interfere
+   * with “normal” dollars in text.
+   * If you turn this off, you can use two or more dollars for text math.
+   */
+  singleDollarTextMath?: boolean | null | undefined
+}
+
+/**
+ * Augment types.
+ */
 declare module 'micromark-util-types' {
+  /**
+   * Compile data.
+   */
+  interface CompileData {
+    mathFlowOpen?: boolean
+  }
+
+  /**
+   * Token types.
+   */
   interface TokenTypeMap {
     mathFlow: 'mathFlow'
     mathFlowFence: 'mathFlowFence'
@@ -13,8 +58,4 @@ declare module 'micromark-util-types' {
     mathTextPadding: 'mathTextPadding'
     mathTextSequence: 'mathTextSequence'
   }
-
-  interface CompileData {
-    mathFlowOpen?: boolean
-  }
 }
diff --git a/dev/lib/html.js b/dev/lib/html.js
index fd525c3..635d8df 100644
--- a/dev/lib/html.js
+++ b/dev/lib/html.js
@@ -1,15 +1,6 @@
 /**
- * @typedef {import('katex').KatexOptions} KatexOptions
- * @typedef {import('micromark-util-types').HtmlExtension} HtmlExtension
- */
-
-/**
- * @typedef {Omit<KatexOptions, 'displayMode'>} Options
- *   Configuration for HTML output.
- *
- *   > 👉 **Note**: passed to `katex.renderToString`.
- *   > `displayMode` is overwritten by this plugin, to `false` for math in
- *   > text (inline), and `true` for math in flow (block).
+ * @import {HtmlOptions as Options} from 'micromark-extension-math'
+ * @import {HtmlExtension} from 'micromark-util-types'
  */
 
 import katex from 'katex'
diff --git a/dev/lib/math-flow.js b/dev/lib/math-flow.js
index 884fb8d..8f0d6a0 100644
--- a/dev/lib/math-flow.js
+++ b/dev/lib/math-flow.js
@@ -1,8 +1,5 @@
 /**
- * @typedef {import('micromark-util-types').Construct} Construct
- * @typedef {import('micromark-util-types').State} State
- * @typedef {import('micromark-util-types').TokenizeContext} TokenizeContext
- * @typedef {import('micromark-util-types').Tokenizer} Tokenizer
+ * @import {Construct, State, TokenizeContext, Tokenizer} from 'micromark-util-types'
  */
 
 import {ok as assert} from 'devlop'
diff --git a/dev/lib/math-text.js b/dev/lib/math-text.js
index b1dece5..89bc08b 100644
--- a/dev/lib/math-text.js
+++ b/dev/lib/math-text.js
@@ -1,21 +1,6 @@
 /**
- * @typedef {import('micromark-util-types').Construct} Construct
- * @typedef {import('micromark-util-types').TokenizeContext} TokenizeContext
- * @typedef {import('micromark-util-types').Tokenizer} Tokenizer
- * @typedef {import('micromark-util-types').Previous} Previous
- * @typedef {import('micromark-util-types').Resolver} Resolver
- * @typedef {import('micromark-util-types').State} State
- * @typedef {import('micromark-util-types').Token} Token
- *
- * @typedef Options
- *   Configuration.
- * @property {boolean | null | undefined} [singleDollarTextMath=true]
- *   Whether to support math (text) with a single dollar (default: `true`).
- *
- *   Single dollars work in Pandoc and many other places, but often interfere
- *   with “normal” dollars in text.
- *   If you turn this off, you can use two or more dollars for text math.
-
+ * @import {Options} from 'micromark-extension-math'
+ * @import {Construct, Previous, Resolver, State, Token, TokenizeContext, Tokenizer} from 'micromark-util-types'
  */
 
 // To do: next major: clean spaces in HTML compiler.
diff --git a/dev/lib/syntax.js b/dev/lib/syntax.js
index 4253f03..501ad98 100644
--- a/dev/lib/syntax.js
+++ b/dev/lib/syntax.js
@@ -1,6 +1,6 @@
 /**
- * @typedef {import('micromark-util-types').Extension} Extension
- * @typedef {import('./math-text.js').Options} Options
+ * @import {Options} from 'micromark-extension-math'
+ * @import {Extension} from 'micromark-util-types'
  */
 
 import {codes} from 'micromark-util-symbol'
diff --git a/package.json b/package.json
index 646cb7a..97d19f1 100644
--- a/package.json
+++ b/package.json
@@ -89,10 +89,25 @@
     "overrides": [
       {
         "files": [
-          "**/*.ts"
+          "**/*.d.ts"
         ],
         "rules": {
-          "@typescript-eslint/consistent-type-definitions": "off"
+          "@typescript-eslint/array-type": [
+            "error",
+            {
+              "default": "generic"
+            }
+          ],
+          "@typescript-eslint/ban-types": [
+            "error",
+            {
+              "extendDefaults": true
+            }
+          ],
+          "@typescript-eslint/consistent-type-definitions": [
+            "error",
+            "interface"
+          ]
         }
       }
     ],