← Language detection: all libraries · Reader board
langdetect vs fast-langdetect: which one detects the language right more often?
langdetect 1.0.9 and fast-langdetect 1.1.0 on the same 760 texts with a known language: 570 single sentences and 190 short paragraphs in 38 languages, from Tatoeba from Language test set (Tatoeba sentences, 38 languages). Measured, not opinion; re-tested by itself on every new PyPI release. Updated 06 November 2026.
More detected correctlyfast-langdetect93.4% vs 93.0%
Faster on this setlangdetect1.3 s vs 1.5 s total (about as fast)
Both read760only langdetect: 0 · only fast-langdetect: 0
fast-langdetect got the language right more often: 93.4% vs 93.0%. langdetect broke (error, hang or crash) on 0 files that fast-langdetect read; fast-langdetect broke on 0 files that langdetect read.
| Library | Text from | 🔴 Fails where the other reads | 🟡 Empty where the other reads | ⏱ Hangs or crashes | ✅ Correct | Median ms/file | Total seconds |
|---|---|---|---|---|---|---|---|
| langdetect 1.0.9 | 760 | 0 | 0 | 0 | 93.0% | 1 | 1.3 |
| fast-langdetect 1.1.0 | 760 | 0 | 0 | 0 | 93.4% | <1 | 1.5 |
By kind of text: share correct
| Texts | langdetect | fast-langdetect |
|---|---|---|
| paragraphs 190 texts | 99.5% | 95.8% |
| short-sentences 570 texts | 90.9% | 92.6% |
Files only langdetect reads (0)
None.
Files only fast-langdetect reads (0)
None.
What this does not tell you
This compares not breaking: whether each library gets any text out of each file. It does not rank text quality (reading order, tables, headings), and speed is one GitHub-hosted runner, default settings, no OCR switched on. If you need structure for RAG, also look at the output on your own files.
How this is measured
- Each library runs a short recipe from its own docs (board/targets.py):
open the file, get all text. Installed with the extras the docs recommend for reading
(
pypdf[full]: AES decryption, Brotli), nothing else. One worker process per CPU; per file 60 s / 120 s / 180 s / 300 s / 600 s at most (the any-document table allows longer: some tools load models), killed above the memory limit. - Fails where another reads: the library raised an error, hung or crashed on a file from which another library in the same table got text. Files that every library fails on (encrypted, truncated, fuzzed) are not counted against anyone.
- Empty where another reads: no error, but no text. This is often the recipe, not the library: for example
python-docx's paragraphs+tables recipe skips headers, text boxes and nested tables. Check the file list. - Any document → text: a file type the tool's docs don't list, or that the tool itself rejects as unsupported, counts as "not supported", not as a failure (lists in board/libs.json). Returning a file's raw RTF source counts as empty, for every tool. Each tool runs with default settings: no OCR switched on by hand.
- OCR: each image comes with the human-written ground-truth text published with its dataset. Words found is the share of its words that appear anywhere in the engine's output (reading order doesn't matter); an image that fails or comes back empty counts as 0. The ground truth of receipts and document pages covers only their annotated text, so a character error rate would punish engines for reading more than was annotated; it is in the raw results but not ranked. English models, CPU, default settings.
- Speech: each clip comes with its dataset's reference transcript. Both texts go through Whisper's English text normalizer (case, punctuation, "twenty" = "20"); word error rate is all substituted, missing and extra words over all reference words, the usual corpus-level WER. A clip that fails or comes back empty counts all its words as errors. The three Whisper implementations use the same base.en model; each other engine its documented default model. English, CPU, default decoding settings.
- Language detection: each text's language is known from Tatoeba. An answer counts as correct if the library's code matches after mapping variants to ISO 639-1 (zh-cn → zh, nb → no, iw → he). Close languages count as different: Croatian detected as Bosnian or Serbian, or Norwegian as Danish, is wrong. One call per text with default settings and all languages enabled.
- PDF → Markdown: pages from AI2's olmOCR-bench (ODC-BY), scored with its own checks (vendored, Apache-2.0): a sentence must be present, a page header or footer absent, two passages in the right order, a table cell next to the right neighbour. Checks passed is all passed checks over all checks; a page that fails or comes back empty passes none. Math pages are left out (their checks need a browser to render formulas). Default settings: whatever OCR a tool does on its own, it does.
- Text quality (order, tables, layout) is not ranked in the other tables; they are about not breaking. The raw results have every output's size and hash.
- Same files for every version: the test collections are pinned to one commit. GitHub-hosted runner, so times are comparable within one table, roughly.