Grammarly Rate Limits

Overview

Grammarly's Text API enforces plan-dependent rate limits across its writing score, AI detection, and plagiarism endpoints. The plagiarism checker is asynchronous and requires polling, which adds complexity to rate management. Token endpoints are separately throttled at roughly 10 requests per hour, so credential rotation during high-throughput batch processing of documents (e.g., scanning an entire content library) requires careful token lifecycle management to avoid auth-layer 429s on top of API-layer throttling.

Rate Limit Reference

Rate Limiter Implementation

class GrammarlyRateLimiter {
  private tokens: number;
  private lastRefill: number;
  private readonly max: number;
  private readonly refillRate: number;
  private queue: Array<{ resolve: () => void }> = [];

  constructor(maxPerMinute: number) {
    this.max = maxPerMinute;
    this.tokens = maxPerMinute;
    this.lastRefill = Date.now();
    this.refillRate = maxPerMinute / 60_000;
  }

  async acquire(): Promise<void> {
    this.refill();
    if (this.tokens >= 1) { this.tokens -= 1; return; }
    return new Promise(resolve => this.queue.push({ resolve }));
  }

  private refill() {
    const now = Date.now();
    this.tokens = Math.min(this.max, this.tokens + (now - this.lastRefill) * this.refillRate);
    this.lastRefill = now;
    while (this.tokens >= 1 && this.queue.length) {
      this.tokens -= 1;
      this.queue.shift()!.resolve();
    }
  }
}

const scoreLimiter = new GrammarlyRateLimiter(90);
const plagiarismLimiter = new GrammarlyRateLimiter(25);

Retry Strategy

async function grammarlyRetry<T>(
  limiter: GrammarlyRateLimiter, fn: () => Promise<Response>, maxRetries = 3
): Promise<T> {
  for (let attempt = 0; attempt <= maxRetries; attempt++) {
    await limiter.acquire();
    const res = await fn();
    if (res.ok) return res.json();
    if (res.status === 429) {
      const retryAfter = parseInt(res.headers.get("Retry-After") || "20", 10);
      const jitter = Math.random() * 2000;
      await new Promise(r => setTimeout(r, retryAfter * 1000 + jitter));
      continue;
    }
    if (res.status >= 500 && attempt < maxRetries) {
      await new Promise(r => setTimeout(r, Math.pow(2, attempt) * 1500));
      continue;
    }
    throw new Error(`Grammarly API ${res.status}: ${await res.text()}`);
  }
  throw new Error("Max retries exceeded");
}

Batch Processing

async function batchScoreDocuments(documents: string[], batchSize = 8) {
  const results: any[] = [];
  for (let i = 0; i < documents.length; i += batchSize) {
    const batch = documents.slice(i, i + batchSize);
    const batchResults = await Promise.all(
      batch.map(text => grammarlyRetry(scoreLimiter, () =>
        fetch("https://api.grammarly.com/ecosystem/api/v2/scores", {
          method: "POST", headers,
          body: JSON.stringify({ text }),
        })
      ))
    );
    results.push(...batchResults);
    if (i + batchSize < documents.length) await new Promise(r => setTimeout(r, 5000));
  }
  return results;
}

Error Handling

Resources

• Grammarly Developer API

Next Steps

See grammarly-performance-tuning.