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

Endpoint	Limit	Window	Scope
Writing score	100 req (Business)	1 minute	Per API key
AI content detection	60 req (Business)	1 minute	Per API key
Plagiarism check (submit)	30 req	1 minute	Per API key
Plagiarism check (poll)	120 req	1 minute	Per API key
Token refresh	10 req	1 hour	Per client credentials

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

Issue	Cause	Fix
429 on writing score	Exceeded plan-tier per-minute cap	Reduce concurrency, use Retry-After
429 on token refresh	More than 10 refreshes/hour	Cache token, refresh only on 401
Plagiarism poll timeout	Result not ready after 60s	Increase poll interval to 10s, max 5 min
413 on large document	Text exceeds 100K character limit	Split into sections, score individually
Empty score response	Text too short for analysis	Validate minimum 50 characters before submission

Prerequisites

• An approved per-operation quota, observed response-header baseline, and a sandbox workload containing fictitious text only.
• Idempotency keys for writes, a bounded queue, and a reviewed recovery path for exhausted work.
• A caller scope that cannot be broadened merely to evade throttling.

Instructions

1. Classify requests as read or write and apply per-scope concurrency limits before dispatch.
2. Honor server retry guidance where present; otherwise use bounded exponential backoff with jitter and a maximum attempt count.
3. Never replay a text-changing request without its idempotency key, and defer nonessential work before the queue threatens freshness.
4. Monitor aggregate limited/deferred counts and canary success, tuning one scope at a time with a rollback to the prior limits.
5. Route exhausted work to reviewed recovery instead of silently dropping or duplicating it.

Output

Return a rate-limit receipt with operation scope, request/limited/deferred counts, retry-policy revision, idempotency outcome, queue state, canary result, and rollback reference. Omit credentials and text payloads.

Examples

scope=sandbox-check; requested=100; limited=3; deferred=3; retry=v2; idempotent=pass; queue=healthy; rollback=limits-r7 proves bounded handling.

Resources

• Grammarly Developer API

Next Steps

See grammarly-performance-tuning.