diff --git a/src/tools/agent/executors.test.ts b/src/tools/agent/executors.test.ts
index c5bddbb..1b4923a 100644
--- a/src/tools/agent/executors.test.ts
+++ b/src/tools/agent/executors.test.ts
@@ -74,6 +74,11 @@ describe('executor registry', () => {
     expect(scopeExecutors('draw a bar chart of my sales').map(e => e.toolId)).toContain('canvas-draw');
     expect(scopeExecutors('plot these data points on a canvas').map(e => e.toolId)).toContain('canvas-draw');
   });
+  it('scopes the data interpreter (peek-data / run-on-data)', () => {
+    expect(scopeExecutors('preview this csv file').map(e => e.toolId)).toContain('peek-data');
+    expect(scopeExecutors('filter rows where amount is over 100 in this csv').map(e => e.toolId)).toContain('run-on-data');
+    expect(scopeExecutors('pivot this data by region').map(e => e.toolId)).toContain('run-on-data');
+  });
   it('does not scope any media compressor for small talk', () => {
     expect(scopeExecutors('hello how are you today')).toEqual([]);
   });
diff --git a/src/tools/agent/executors.ts b/src/tools/agent/executors.ts
index fbc813b..51eb513 100644
--- a/src/tools/agent/executors.ts
+++ b/src/tools/agent/executors.ts
@@ -403,6 +403,34 @@ export const AGENT_EXECUTORS: AgentExecutor[] = [
       return { text: `Words: ${s.words}\nCharacters: ${s.characters} (${s.charactersNoSpaces} without spaces)\nSentences: ${s.sentences}\nParagraphs: ${s.paragraphs}\nLines: ${s.lines}\nReading time: ~${s.readingMinutes} min` };
     },
   },
+  {
+    // v3 data interpreter: peek the schema so the model writes a correct transform.
+    toolId: 'peek-data', page: 'csv-json',
+    description: "Preview a data file's shape (dimensions + first rows). Call this FIRST when the user wants to clean/filter/reshape a data file, so you can see the columns before writing a transform.",
+    match: re(/(peek|preview|inspect|look at|show me|what.?s? in).*(data|csv|file|rows?|columns?)|what columns/i),
+    files: [{ key: 'file', accept: '.csv,.tsv,.txt,.json,text/*', label: 'Data file' }], params: [],
+    execute: async ({ files }) => {
+      const { peekData } = await import('@/tools/documents/data-run.lib');
+      return { text: peekData(await files.file.text()) };
+    },
+  },
+  {
+    toolId: 'run-on-data', page: 'code-scratchpad',
+    description: "Transform a data file by writing JavaScript. YOU write JS in `code` that reads the file's text as `input` and returns the result (assign to `output` or return it). Helpers: parseCSV(text)->rows[][], toCSV(rows)->text, JSON. Runs in a no-network sandbox. Call peek-data first to see the columns. CSV output chains to spreadsheet-convert for Excel.",
+    match: re(/(clean|filter|dedup|deduplicate|sort|pivot|group|reshape|transform|process|extract|merge|remove|summari[sz]e|aggregate).*(csv|data|rows?|records?|file|columns?|json)|(csv|data|rows?|spreadsheet|json).*(clean|filter|dedup|sort|pivot|group|reshape|transform|process|extract|remove|aggregate)/i),
+    files: [{ key: 'file', accept: '.csv,.tsv,.txt,.json,text/*', label: 'Data file' }],
+    params: [{ key: 'code', type: 'string', label: 'JavaScript transform (reads `input`, returns the output text)' }],
+    execute: async ({ files, params }, onProgress) => {
+      const { runDataCode } = await import('@/tools/documents/data-run.lib');
+      const { extractCode } = await import('@/tools/image/canvas-run.lib');
+      const code = extractCode(String(params.code ?? ''));
+      if (!code) throw new Error('no transform code — write JS that reads `input` and returns the result');
+      onProgress?.(0.3);
+      const out = await runDataCode(code, await files.file.text());
+      const isJson = out.trim().startsWith('{') || out.trim().startsWith('[');
+      return { blob: new Blob([out], { type: isJson ? 'application/json' : 'text/csv' }), filename: isJson ? 'output.json' : 'output.csv', text: `transformed the data (${out.length} chars)` };
+    },
+  },
   {
     toolId: 'hash-text', description: 'Hash text (SHA-256)', match: re(/\bhash\b|sha-?\d|md5|checksum|digest/i),
     files: [], params: [{ key: 'text', type: 'string', label: 'Text' }],
diff --git a/src/tools/documents/data-run.lib.test.ts b/src/tools/documents/data-run.lib.test.ts
new file mode 100644
index 0000000..40ea527
--- /dev/null
+++ b/src/tools/documents/data-run.lib.test.ts
@@ -0,0 +1,18 @@
+import { describe, it, expect } from 'vitest';
+import { peekData } from './data-run.lib';
+
+describe('peekData', () => {
+  it('reports CSV dimensions and shows the first rows', () => {
+    const out = peekData('name,qty\nApple,3\nBanana,5\nCherry,2');
+    expect(out).toMatch(/4 lines, ~2 columns \(CSV\)/);
+    expect(out).toContain('name,qty');
+    expect(out).toContain('Apple,3');
+  });
+  it('truncates long inputs with an ellipsis', () => {
+    const many = Array.from({ length: 40 }, (_, i) => `row${i}`).join('\n');
+    const out = peekData(many, 5);
+    expect(out).toContain('row0');
+    expect(out).toContain('…');
+    expect(out).not.toContain('row30');
+  });
+});
diff --git a/src/tools/documents/data-run.lib.ts b/src/tools/documents/data-run.lib.ts
new file mode 100644
index 0000000..746755d
--- /dev/null
+++ b/src/tools/documents/data-run.lib.ts
@@ -0,0 +1,39 @@
+/**
+ * Host side of the data interpreter. `peekData` builds a small schema sample the
+ * model reads before writing a transform (pure/testable); `runDataCode` runs the
+ * code in the sandbox worker with a timeout (needs a real browser).
+ */
+
+/** A compact preview of a file's shape: dimensions + the first rows. */
+export function peekData(text: string, maxLines = 15): string {
+  const lines = text.replace(/\r\n/g, '\n').split('\n').filter((l, i, a) => i < a.length - 1 || l.length > 0);
+  const head = lines.slice(0, maxLines);
+  const looksCsv = /,/.test(head[0] ?? '');
+  const cols = looksCsv ? (head[0]?.split(',').length ?? 0) : 0;
+  const meta = `${lines.length} line${lines.length === 1 ? '' : 's'}` + (looksCsv ? `, ~${cols} columns (CSV)` : '');
+  return `${meta}\n\nFirst ${head.length} line${head.length === 1 ? '' : 's'}:\n${head.join('\n')}${lines.length > maxLines ? '\n…' : ''}`;
+}
+
+export interface DataRunOpts { timeoutMs?: number }
+
+/** Run a data-transform in the sandbox worker; resolve with the output text. */
+export async function runDataCode(code: string, input: string, opts: DataRunOpts = {}): Promise<string> {
+  if (typeof Worker === 'undefined') throw new Error('this browser cannot run the data sandbox');
+  const timeoutMs = opts.timeoutMs ?? 8000;
+  const worker = new Worker(new URL('./data-sandbox.worker.ts', import.meta.url), { type: 'module' });
+  try {
+    return await new Promise<string>((resolve, reject) => {
+      const timer = setTimeout(() => reject(new Error('the transform timed out — possible infinite loop')), timeoutMs);
+      worker.onmessage = (e: MessageEvent) => {
+        clearTimeout(timer);
+        const d = e.data as { ok: boolean; output?: string; error?: string };
+        if (d.ok && typeof d.output === 'string') resolve(d.output);
+        else reject(new Error(d.error || 'transform failed'));
+      };
+      worker.onerror = ev => { clearTimeout(timer); reject(new Error(ev.message || 'sandbox error')); };
+      worker.postMessage({ code, input });
+    });
+  } finally {
+    worker.terminate();
+  }
+}
diff --git a/src/tools/documents/data-sandbox.worker.ts b/src/tools/documents/data-sandbox.worker.ts
new file mode 100644
index 0000000..d340fa9
--- /dev/null
+++ b/src/tools/documents/data-sandbox.worker.ts
@@ -0,0 +1,48 @@
+/**
+ * Sandbox for running LLM-written DATA-transform code (agent v3 "data interpreter").
+ *
+ * Same lock-down as the canvas sandbox: a Web Worker (no DOM), with the
+ * exfiltration/storage channels neutered, and a wall-clock timeout enforced by
+ * the main thread. The code gets the file's text as `input` plus small CSV/JSON
+ * helpers, and returns the transformed text.
+ */
+
+const blocked = () => { throw new Error('disabled in the data sandbox'); };
+for (const key of ['fetch', 'XMLHttpRequest', 'WebSocket', 'importScripts', 'indexedDB', 'caches', 'EventSource', 'SharedWorker', 'Worker', 'Notification']) {
+  try { Object.defineProperty(self, key, { value: blocked, writable: false, configurable: false }); } catch { /* non-configurable */ }
+}
+
+/** Parse a CSV line into fields, honoring double-quoted cells. */
+function splitCsvLine(line: string): string[] {
+  const out: string[] = [];
+  let cur = '', inQ = false;
+  for (let i = 0; i < line.length; i++) {
+    const c = line[i];
+    if (inQ) {
+      if (c === '"') { if (line[i + 1] === '"') { cur += '"'; i++; } else inQ = false; }
+      else cur += c;
+    } else if (c === '"') inQ = true;
+    else if (c === ',') { out.push(cur); cur = ''; }
+    else cur += c;
+  }
+  out.push(cur);
+  return out;
+}
+const parseCSV = (text: string): string[][] => text.replace(/\r\n/g, '\n').replace(/\n+$/, '').split('\n').map(splitCsvLine);
+const toCSV = (rows: unknown[][]): string =>
+  rows.map(r => r.map(c => { const s = String(c ?? ''); return /[",\n]/.test(s) ? `"${s.replace(/"/g, '""')}"` : s; }).join(',')).join('\n');
+
+self.onmessage = async (e: MessageEvent<{ code: string; input: string }>) => {
+  const { code, input } = e.data;
+  const post = (msg: unknown) => (self as unknown as Worker).postMessage(msg);
+  try {
+    // The code sees `input` (file text) + helpers, and returns the output string.
+    const fn = new Function('input', 'parseCSV', 'toCSV', 'JSON', 'Math', 'Date',
+      `"use strict";\nlet output;\n${code}\n;return (typeof output !== 'undefined') ? output : undefined;`);
+    let out = await fn(input, parseCSV, toCSV, JSON, Math, Date);
+    if (out === undefined || out === null) throw new Error('the code produced no output — set `output` or return a value');
+    post({ ok: true, output: typeof out === 'string' ? out : JSON.stringify(out, null, 2) });
+  } catch (err) {
+    post({ ok: false, error: err instanceof Error ? err.message : String(err) });
+  }
+};