@web-ai-sdk/rewriter

web-ai-sdk building block for the Web’s Built-in Rewriter API. Revises and restructures existing text with tone / length adjustments, session reuse, streaming, and opt-in result caching.

Status

The Rewriter API is in a developer trial (origin trial) in Chrome 137 to 148. It shares the Writer’s joint trial, so it’s enabled via the same chrome://flags/#writer-api-for-gemini-nano flag on localhost (there is no separate Rewriter flag; chrome://flags/#optimization-guide-on-device-model must also be enabled). In Edge it’s a developer preview in Canary/Dev 138+ behind “Rewriter API for Phi mini”. On any other browser this library is a no-op for the React hook (it stays in "unavailable"). The vanilla rewrite() throws RewriterUnavailableError so callers can branch explicitly.

Install

pnpm add @web-ai-sdk/rewriter
# or: npm i @web-ai-sdk/rewriter / bun add @web-ai-sdk/rewriter

The React adapter ships as a subpath export, with no extra install. react is a peer dependency only when you import the /react entry.

Vanilla TypeScript / DOM

import { rewrite } from "@web-ai-sdk/rewriter";

const result = await rewrite({
  input: "hey, can u send me that doc when u get a sec? thx",
  tone: "more-formal",
  length: "as-is",
  onUpdate: (text) => console.log("partial", text),
});

console.log(result.output, result.cached);

result.output is the rewritten text (trimmed), or null when the input is empty.

React

import { useRewriter } from "@web-ai-sdk/rewriter/react";

export function Polish({ draft }: { draft: string }) {
  const { status, output } = useRewriter({ input: draft, tone: "more-formal" });

  if (status === "unavailable") return null;
  if (status === "loading") return <p>Rewriting…</p>;
  return <p>{output}</p>;
}

State machine: idle | loading | streaming | done | unavailable. output is the latest text (grows during streaming). fromCache is true when the result came back without invoking the model.

API

`rewrite(options): Promise<RewriteResult>`

interface RewriteOptions {
  input: string;                  // text to rewrite
  context?: string;               // per-call background info
  language?: string;              // BCP-47; drives input/output hints when supported
  supportedLanguages?: readonly string[]; // default ["en", "es", "ja"]
  tone?: "as-is" | "more-formal" | "more-casual";   // default "as-is"
  format?: "as-is" | "markdown" | "plain-text";     // default "as-is"
  length?: "as-is" | "shorter" | "longer";          // default "as-is"
  sharedContext?: string;
  monitor?: (m: CreateMonitor) => void;
  cache?: "session" | "local" | { get, set };
  cacheKey?: string;
  onUpdate?: (text: string) => void; // cumulative buffer, not deltas
  signal?: AbortSignal;
}

interface RewriteResult {
  output: string | null;
  cached: boolean;
}

`isAvailable(): boolean`

Feature-detect helper.

`checkAvailability(options?): Promise<RewriterAvailability | null>`

Forwards to the spec’s availability() call. Returns null if the global is missing or the call throws.

Cache controls

import {
  clearRewriterSessions,    // drop every cached rewriter session
  clearRewriterSession,     // drop one cached session by create-options
  configureRewriterCache,   // change the LRU cap (default 8)
} from "@web-ai-sdk/rewriter";

The internal session cache is LRU-bounded (default 8). Evicted sessions have their destroy() invoked when present.

Output normalization

The wrapper trims leading/trailing whitespace only, so internal markdown formatting and line breaks the model produces stay intact.