diff --git a/main.ts b/main.ts
index 3f10a46..a174902 100644
--- a/main.ts
+++ b/main.ts
@@ -1,7 +1,4 @@
-import { lint } from './src/lint';
+import { MarkEdit } from 'markedit-api';
+import { proofreadingExtension } from './src/extension';
 
-(async () => {
-  // For testing purpose only
-  const results = lint('Helllo, is this something you want?');
-  console.log(results);
-})();
+MarkEdit.addExtension(proofreadingExtension());
diff --git a/src/decoration.ts b/src/decoration.ts
new file mode 100644
index 0000000..b2dcfd4
--- /dev/null
+++ b/src/decoration.ts
@@ -0,0 +1,84 @@
+import { EditorView, Decoration } from '@codemirror/view';
+import type { DecorationSet } from '@codemirror/view';
+import { StateField, StateEffect } from '@codemirror/state';
+import { SuggestionKind } from 'harper.js';
+import type { Lint, Suggestion } from 'harper.js';
+
+export interface Diagnostic {
+  from: number;
+  to: number;
+  title: string;
+  message: string;
+  actions: DiagnosticAction[];
+}
+
+export interface DiagnosticAction {
+  name: string;
+  apply: (view: EditorView, from: number, to: number) => void;
+}
+
+export const setDiagnosticsEffect = StateEffect.define<Diagnostic[]>();
+
+export const diagnosticsField = StateField.define<{ diagnostics: Diagnostic[]; decorations: DecorationSet }>({
+  create() {
+    return { diagnostics: [], decorations: Decoration.none };
+  },
+  update(value, tr) {
+    if (tr.docChanged && value.decorations !== Decoration.none) {
+      value = { diagnostics: value.diagnostics, decorations: value.decorations.map(tr.changes) };
+    }
+
+    for (const effect of tr.effects) {
+      if (effect.is(setDiagnosticsEffect)) {
+        const diagnostics = effect.value;
+        const ranges = diagnostics
+          .filter(d => d.from < d.to)
+          .map(d => Decoration.mark({ class: 'cm-harper-lint' }).range(d.from, d.to));
+
+        value = { diagnostics, decorations: Decoration.set(ranges, true) };
+      }
+    }
+
+    return value;
+  },
+  provide: f => EditorView.decorations.from(f, val => val.decorations),
+});
+
+export function lintToDiagnostic(l: Lint): Diagnostic {
+  const span = l.span();
+
+  return {
+    from: span.start,
+    to: span.end,
+    title: l.lint_kind_pretty(),
+    message: l.message(),
+    actions: l.suggestions().map(suggestionToAction),
+  };
+}
+
+function suggestionToAction(sug: Suggestion): DiagnosticAction {
+  const kind = sug.kind();
+  const replacement = sug.get_replacement_text();
+
+  let name: string;
+  if (kind === SuggestionKind.Remove) {
+    name = 'Remove';
+  } else if (kind === SuggestionKind.InsertAfter) {
+    name = `Insert "${replacement}"`;
+  } else {
+    name = replacement;
+  }
+
+  return {
+    name,
+    apply(view, from, to) {
+      if (kind === SuggestionKind.Remove) {
+        view.dispatch({ changes: { from, to, insert: '' }, selection: { anchor: from } });
+      } else if (kind === SuggestionKind.Replace) {
+        view.dispatch({ changes: { from, to, insert: replacement }, selection: { anchor: from + replacement.length } });
+      } else if (kind === SuggestionKind.InsertAfter) {
+        view.dispatch({ changes: { from: to, to, insert: replacement }, selection: { anchor: to + replacement.length } });
+      }
+    },
+  };
+}
diff --git a/src/extension.ts b/src/extension.ts
new file mode 100644
index 0000000..531098e
--- /dev/null
+++ b/src/extension.ts
@@ -0,0 +1,49 @@
+import { ViewPlugin } from '@codemirror/view';
+import type { ViewUpdate } from '@codemirror/view';
+import type { Extension } from '@codemirror/state';
+import { EditorView } from '@codemirror/view';
+import { diagnosticsField, setDiagnosticsEffect, lintToDiagnostic } from './decoration';
+import { lintTooltip } from './tooltip';
+import { baseTheme } from './styling';
+import { lint } from './lint';
+
+const lintDelay = 500;
+
+const lintScheduler = ViewPlugin.fromClass(class {
+  private timeout: ReturnType<typeof setTimeout> | undefined;
+
+  constructor(readonly view: EditorView) {
+    this.scheduleLint();
+  }
+
+  update(update: ViewUpdate) {
+    if (update.docChanged) {
+      this.scheduleLint();
+    }
+  }
+
+  scheduleLint() {
+    clearTimeout(this.timeout);
+    this.timeout = setTimeout(() => { void this.runLint(); }, lintDelay);
+  }
+
+  async runLint() {
+    const doc = this.view.state.doc;
+    const text = doc.sliceString(0);
+    const lints = await lint(text);
+
+    if (this.view.state.doc !== doc) {
+      return;
+    }
+
+    this.view.dispatch({ effects: setDiagnosticsEffect.of(lints.map(lintToDiagnostic)) });
+  }
+
+  destroy() {
+    clearTimeout(this.timeout);
+  }
+});
+
+export function proofreadingExtension(): Extension {
+  return [diagnosticsField, lintScheduler, lintTooltip, baseTheme];
+}
diff --git a/src/lint.ts b/src/lint.ts
index 565eb38..d1b6e9e 100644
--- a/src/lint.ts
+++ b/src/lint.ts
@@ -1,14 +1,6 @@
 import { LocalLinter, binaryInlined } from 'harper.js';
 
-const linter = new LocalLinter({
-  binary: binaryInlined,
-});
-
-linter.lint('Helllo, is this something you want?').then(results => {
-  for (const result of results) {
-    console.log(result.suggestions());
-  }
-});
+const linter = new LocalLinter({ binary: binaryInlined });
 
 export async function lint(text: string) {
   return await linter.lint(text);
diff --git a/src/styling.ts b/src/styling.ts
new file mode 100644
index 0000000..f2e5de5
--- /dev/null
+++ b/src/styling.ts
@@ -0,0 +1,56 @@
+import { EditorView } from '@codemirror/view';
+
+export const baseTheme = EditorView.baseTheme({
+  '.cm-harper-lint': {
+    backgroundImage: 'url("data:image/svg+xml,%3Csvg xmlns=\'http://www.w3.org/2000/svg\' width=\'6\' height=\'3\'%3E%3Cpath d=\'m0 3 l2 -2 l1 0 l2 2 l1 0\' stroke=\'%23d4a017\' fill=\'none\' stroke-width=\'.7\'/%3E%3C/svg%3E")',
+    backgroundRepeat: 'repeat-x',
+    backgroundPosition: 'bottom',
+    paddingBottom: '0.7px',
+  },
+  '.cm-harper-tooltip': {
+    padding: '4px 8px',
+    maxWidth: '400px',
+  },
+  '.cm-harper-diagnostic + .cm-harper-diagnostic': {
+    marginTop: '8px',
+    paddingTop: '8px',
+    borderTop: '1px solid #ddd',
+  },
+  '.cm-harper-title': {
+    fontWeight: 'bold',
+    marginBottom: '2px',
+    fontSize: '13px',
+  },
+  '.cm-harper-message': {
+    fontSize: '12px',
+    lineHeight: '1.4',
+    marginBottom: '4px',
+  },
+  '.cm-harper-actions': {
+    display: 'flex',
+    flexWrap: 'wrap',
+    gap: '4px',
+  },
+  '.cm-harper-action': {
+    padding: '2px 8px',
+    border: '1px solid #ccc',
+    borderRadius: '4px',
+    background: '#f5f5f5',
+    cursor: 'pointer',
+    fontSize: '12px',
+    '&:hover': {
+      background: '#e0e0e0',
+    },
+  },
+  '&dark .cm-harper-diagnostic + .cm-harper-diagnostic': {
+    borderTopColor: '#444',
+  },
+  '&dark .cm-harper-action': {
+    borderColor: '#555',
+    background: '#333',
+    color: '#eee',
+    '&:hover': {
+      background: '#444',
+    },
+  },
+});
diff --git a/src/tooltip.ts b/src/tooltip.ts
new file mode 100644
index 0000000..7bed160
--- /dev/null
+++ b/src/tooltip.ts
@@ -0,0 +1,65 @@
+import { hoverTooltip } from '@codemirror/view';
+import { diagnosticsField } from './decoration';
+
+export const lintTooltip = hoverTooltip((view, pos, side) => {
+  const { diagnostics } = view.state.field(diagnosticsField);
+  const found = diagnostics.filter(d =>
+    pos >= d.from && pos <= d.to &&
+    (pos > d.from || side > 0) &&
+    (pos < d.to || side < 0),
+  );
+
+  if (found.length === 0) {
+    return null;
+  }
+
+  return {
+    pos: found[0].from,
+    end: found[found.length - 1].to,
+    above: true,
+    create(tooltipView) {
+      const dom = document.createElement('div');
+      dom.className = 'cm-harper-tooltip';
+
+      for (const diagnostic of found) {
+        const item = document.createElement('div');
+        item.className = 'cm-harper-diagnostic';
+
+        const title = document.createElement('div');
+        title.className = 'cm-harper-title';
+        title.textContent = diagnostic.title;
+        item.appendChild(title);
+
+        const message = document.createElement('div');
+        message.className = 'cm-harper-message';
+        message.textContent = diagnostic.message;
+        item.appendChild(message);
+
+        if (diagnostic.actions.length > 0) {
+          const actions = document.createElement('div');
+          actions.className = 'cm-harper-actions';
+
+          for (const action of diagnostic.actions) {
+            const button = document.createElement('button');
+            button.className = 'cm-harper-action';
+            button.textContent = action.name;
+            button.onmousedown = (e) => {
+              e.preventDefault();
+              const current = view.state.field(diagnosticsField).diagnostics.find(d => d === diagnostic);
+              if (current) {
+                action.apply(tooltipView, current.from, current.to);
+              }
+            };
+            actions.appendChild(button);
+          }
+
+          item.appendChild(actions);
+        }
+
+        dom.appendChild(item);
+      }
+
+      return { dom };
+    },
+  };
+});