eusgec-wiki-eval — real Basque errors from Wikipedia, hand-checked

The small, honest benchmark behind the numbers on itzune/gector-eus-v5, itzune/gector-eus-v2 and itzune/latxa-8b-gec-lora-v2: 171 real errors and 247 clean sentences taken from actual Basque Wikipedia revisions and manually verified, so the "clean" half really is clean and the "error" half really contains the mistake the editor fixed.

Synthetic error-injection benchmarks flatter GEC models; this one does not.

Composition

config	split	rows	what it is
default	errorful	171	real corrections, labelled by error type
default	clean	247	sentences no editor touched (false-positive control)
review	judged	600	the mined revision pairs these came from, with human verdicts

from datasets import load_dataset

err = load_dataset("itzune/eusgec-wiki-eval", split="errorful")
clean = load_dataset("itzune/eusgec-wiki-eval", split="clean")
print(err[0])   # source, target, error_type, category, ...

Error types in the errorful split

type	n
spelling	52
case	38
punctuation	28
inflection	17
from_clean (regression introduced by an editor)	12
multi	10
word_delete	6
word_insert	5
rewrite	2
word_swap	1

Fields

errorful: id (wk-*), nature (error), category (real), error_type, domain (wikipedia), source, target.

clean: sentence.

review/judged: id, shape (edit shape: spelling, inflection, word_swap, rewrite, multi, …), source, target, change, comment (Wikipedia edit summary), verdict (Y/N — is this a real error?), fixed_target, notes (human notes from the verification pass).

How it was built

1. Mine sentence-level revision pairs from the Basque Wikipedia dump euwiki-20261101, keeping small edits whose corrected sentence survived to the latest revision.
2. Sample pairs across edit shapes; for each, render the original and corrected sentence and record the edit summary.
3. Manually verify every row: does the diff reflect a genuine error (not a rewrite, not vandalism, not a stylistic change)? Rows marked N were dropped from errorful; the review config keeps them so the noise rate of mined Wikipedia edits stays measurable.
4. category = real, domain = wikipedia distinguishes this slice from the synthetic horkonpon slices when pooled.

Every article that contributed here is excluded from itzune/wiki-gec-distill-eu and from the horkonpon Wikipedia configs, so the benchmark stays out of training.

Metrics worth reporting

Score with eusgec eval (the scorer used for the published numbers) or any M²-style scorer:

• exact match on errorful (sentence fully corrected)
• token-level P / R / F0.5 (β = 0.5: a false correction is worse than a miss)
• clean false-positive rate on clean — the number that decides whether a browser assistant is usable

Published reference points (int4 ONNX GECToR unless stated):

system	exact	P	R	F0.5	clean FP
GECToR v2	—	—	—	15.7	0.0%
GECToR v4.1 + cascade	8.2%	55.6	7.9	25.2	0.0%
GECToR v5 + cascade	14.6%	71.7	17.4	44.1	1.2%
latxa-8b-gec-lora-v2, margin −1	28.1%	75.3	30.5	58.2	2.8%

Limitations

• Small: 171 errorful sentences. One sentence = 0.6 points of exact match; differences under ~2 points are noise.
• Wikipedia register only — encyclopedic prose, not news, not social media.
• Labels are single-annotator; the review verdicts are one Basque speaker's judgement, not a multi-annotator consensus.
• Wikipedia corrections include stylistic preferences; from_clean rows keep the handful of "corrections" that introduced an error, which most systems cannot catch and which depress every score slightly.

Licensing and attribution

CC-BY-SA-4.0 — derived from the Basque Wikipedia dump euwiki-20261101. The review config includes edit summaries and revision context from Wikipedia; article titles are intentionally not stored, but the sentences are verbatim Wikipedia content, so attribution to the project and share-alike both apply.

Citation

@misc{ezpeleta2026eusgecwikieval,
  author       = {Xabi Ezpeleta},
  title        = {eusgec-wiki-eval: a hand-checked benchmark of real Basque
                  grammatical errors from Wikipedia},
  year         = {2026},
  publisher    = {Hugging Face},
  howpublished = {\url{https://huggingface.co/datasets/itzune/eusgec-wiki-eval}}
}

References

• Basque Wikipedia dump euwiki-20261101, dumps.wikimedia.org/euwiki (CC-BY-SA-4.0)
• Scorer and baselines: itzune/gector-eus-v2 (scripts/eval_onnx.py, eusgec eval)
• Bryant, C., Felice, M., Briscoe, T. (2017). Automatic Annotation and Evaluation of Error Types in Learner Corpora — M² alignment convention.
• Omelianchuk, K. et al. (2020). GECToR — Tag, Not Rewrite. BEA@ACL. arXiv:2005.12592
• Evaluated systems: itzune/gector-eus-v5, itzune/gector-eus-v2, itzune/latxa-8b-gec-lora-v2