AmberPen vs Sapling
Sapling offers a neural grammar-correction API (/edits) aimed at the same use case as
AmberPen: send text, get back structured edits. We benchmarked both on the same public corpora
and compared list prices.
Benchmark results
Both APIs ran over identical inputs — details and method on the benchmarks page.
| Metric | AmberPen | Sapling |
|---|---|---|
| JFLEG fluency (GLEU, 754 sentences) | 0.561 | 0.470 |
| CWEB precision (6,845 sentences) | 37.4% | 23.6% |
| CWEB recall | 65.5% | 49.1% |
| CWEB ERRANT F0.5 | 40.9 | 26.3 |
AmberPen leads on both benchmarks: it finds more of the annotated errors on real web text and makes fewer unwanted edits — Sapling's lower precision means more than 3 of every 4 edits it proposed on CWEB didn't match a human annotation.
Speed
| Latency (per sentence) | AmberPen | Sapling |
|---|---|---|
| p50 | 217 ms | 620 ms |
| p95 | 1,024 ms | 1,086 ms |
| p99 | 1,413 ms | 1,646 ms |
AmberPen's median response is roughly 3× faster, which matters most for as-you-type checking where the median request is the experience.
Price
Sapling's Edits API is billed per character with volume tiers; AmberPen plans include a character allowance with flat overage. Sapling rates below are for English (Chinese, Japanese, and Korean are billed at 2.5×; AmberPen has no per-language multiplier). AmberPen prices are listed in euros; Sapling prices are listed in US dollars.
| Rate | AmberPen | Sapling Edits |
|---|---|---|
| Entry | Starter — €5 / month, 500K chars included, then €9 / 1M | $0.025 / 1K chars ($25 / 1M) |
| Volume | Pro €49/mo — 9M chars included, then €6 / 1M | $0.020 / 1K from 10M, $0.015 / 1K from 50M |
Example monthly bills
| Characters / month | AmberPen | Sapling |
|---|---|---|
| 1M | €9.50 (Starter) | $25 |
| 5M | €49 (Pro) | $125 |
| 10M | €55 (Pro + overage) | $250 |
| 50M | €295 (Pro + overage, or Scale) | $1,050 |
AmberPen's listed cost is lower at every volume in the table, before currency conversion. Sapling pricing from sapling.ai/docs/api/pricing, July 2026 — check there for current rates. AmberPen pricing is on the pricing page.
This page covers AmberPen and Sapling head to head. If you are still shortlisting, the grammar checker API comparison reviews seven options side by side, grammar checker API pricing compared models the bill across every provider, and how grammar correction is measured explains what the scores above do and do not prove.