Rewriter

Building block for the Web’s Built-in Rewriter API. Revises and restructures existing text with tone / length adjustments, session reuse, streaming, and pluggable result caching. The React adapter lives at @web-ai-sdk/rewriter/react; see useRewriter.

Usage

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) => render(text),
});

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

result.output is the rewritten text (trimmed), or null when the input is empty. result.cached tells you whether the response came from the cache without invoking the model.

Options

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[];
  tone?: "as-is" | "more-formal" | "more-casual";
  format?: "as-is" | "markdown" | "plain-text";
  length?: "as-is" | "shorter" | "longer";
  sharedContext?: string;
  monitor?: (m: CreateMonitor) => void;
  cache?: "session" | "local" | { get, set };
  cacheKey?: string;
  onUpdate?: (text: string) => void;
  signal?: AbortSignal;
}

Name	Type	Description
input required	string	Text to rewrite. Empty / whitespace resolves to { output: null }.
context	string	Optional per-call background information for the model.
language	string	BCP-47 language for input + output hints. Falls back to omitting hints if unsupported.
supportedLanguages	readonly string[]	Languages the model supports for hints. Defaults to ["en", "es", "ja"].
tone	"as-is" | "more-formal" | "more-casual"	Tone adjustment. Defaults to "as-is".
format	"as-is" | "markdown" | "plain-text"	Output format. Defaults to "as-is".
length	"as-is" | "shorter" | "longer"	Length adjustment. Defaults to "as-is".
sharedContext	string	A hint shared across multiple rewrite tasks.
monitor	(m) => void	Observe the first-call model download.
cache	"session" | "local" | { get, set }	Opt-in result cache.
cacheKey	string	Override the default cache key.
onUpdate	(text: string) => void	Streaming update callback. Receives the cumulative buffer, not deltas.
signal	AbortSignal	Abort signal.

Returns

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

Writer vs. Rewriter

The Writer generates new content from a task description; the Rewriter transforms text you already have. They share the same lifecycle (session reuse, streaming, caching) and the same tone / format / length ergonomics, but the Rewriter’s enums are relative adjustments (more-formal, shorter, as-is) rather than absolute targets.

Errors and unavailability

The vanilla rewrite() throws RewriterUnavailableError when the API is missing:

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

try {
  const result = await rewrite({ input: draft, tone: "more-formal" });
} catch (err) {
  if (err instanceof RewriterUnavailableError) return;
  throw err;
}

AbortSignal is supported. Aborting mid-stream resolves cleanly; an opt-in result cache is not written for aborted runs.