README

A free academic writing tool by Plagiarism Checker X.

Plagx Cite for PHP is a free, open-source citation generator and reference checker for PHP and Laravel. It turns sources into correct APA 7 and MLA 9 references and in-text citations, so your app can build a clean reference list in seconds. It also checks the list for duplicate references, broken DOIs and missing details.

Use it as an APA citation generator or MLA citation generator: create a reference list, bibliography or works cited page, generate in-text citations, turn a DOI into a citation, import and export BibTeX, and find duplicate references.

No runtime dependencies, PHP 8.1+
Works in any PHP project, including Laravel, Symfony and WordPress
Uses CSL-JSON, the reference format used by Zotero, Mendeley and Crossref
Plain text, HTML or Markdown output
Same output as the JavaScript version, plagx-cite on npm

Try the live demo →

Developer downloads: Packagist · npm · PyPI · Docker Hub · GitHub

Need a quick citation online? Use the free citation generator.

Plagx Cite is a free academic writing utility by Plagiarism Checker X. It is a citation generator that builds and checks APA and MLA reference lists. Plagiarism checking and AI-generated text detection are available in Plagiarism Checker X, linked at the end of this page.

Install

composer require plagiarismcheckerx/plagx-cite

Quick start

use Plagx\Cite\Cite;

$ref = [
    'type' => 'article-journal',
    'title' => 'Deep learning for text similarity',
    'author' => [['family' => 'Smith', 'given' => 'John Allen'], ['family' => 'Lee', 'given' => 'Kate']],
    'issued' => ['date-parts' => [[2020]]],
    'container-title' => 'Journal of Academic Writing',
    'volume' => '12',
    'issue' => '3',
    'page' => '45-67',
    'DOI' => '10.1234/jaw.2020.045',
];

Cite::formatReference($ref);
// Smith, J. A., & Lee, K. (2020). Deep learning for text similarity. Journal of Academic Writing, 12(3), 45–67. https://doi.org/10.1234/jaw.2020.045

Cite::formatReference($ref, ['style' => 'mla']);
// Smith, John Allen, and Kate Lee. “Deep learning for text similarity.” Journal of Academic Writing, vol. 12, no. 3, 2020, pp. 45-67, https://doi.org/10.1234/jaw.2020.045.

Cite::citeInText($ref, ['page' => '50']);                  // (Smith & Lee, 2020, p. 50)
Cite::citeInText($ref, ['narrative' => true]);             // Smith and Lee (2020)
Cite::citeInText($ref, ['style' => 'mla', 'page' => '50']); // (Smith and Lee 50)

References are plain PHP arrays in CSL-JSON form, so a Zotero or Crossref export works with json_decode($json, true).

API

All methods are static on Plagx\Cite\Cite.

Formatting references and citations

Method	Returns
`formatReference($ref, ['style' => …, 'format' => …])`	One reference-list entry
`formatBibliography($refs, ['style' => …, 'format' => …])`	Sorted list of entries
`citeInText($ref, ['style' => …, 'page' => …, 'narrative' => …])`	In-text citation
`sortReferences($refs)`	New list sorted by author, year, title
`styles()`	`['apa', 'mla']`

style: 'apa' (default) or 'mla'
format: 'text' (default), 'html' (titles in <i>, text escaped) or 'markdown' (titles in *…*)

Supported reference types: article-journal, article-magazine, article-newspaper, book, chapter, paper-conference, report, thesis, webpage. Other types fall back to a sensible general layout.

BibTeX import and export

Cite::toBibTeX([$ref]);
// @article{smith2020deep,
//   author = {Smith, John Allen and Lee, Kate},
//   ...

$refs = Cite::parseBibTeX(file_get_contents('library.bib'));

parseBibTeX handles @string macros, # concatenation, common LaTeX accents ({\"u} → ü), organisation names in braces, and BibLaTeX date / journaltitle fields.

DOI lookup

$ref = Cite::lookupDOI('10.1038/nature14539', ['mailto' => 'you@example.com']);
echo Cite::formatReference($ref);

Cite::normalizeDOI('https://doi.org/10.1038/NATURE14539'); // '10.1038/NATURE14539'
Cite::extractDOIs($text);                                  // every DOI found in the text

lookupDOI calls the free public Crossref API. If a DOI isn't registered with Crossref, such as arXiv or Zenodo DOIs from DataCite, it falls back to doi.org content negotiation. No API key is needed. It uses curl when available, otherwise PHP streams. To use your own HTTP client (for example Guzzle or Laravel's Http), pass 'http' => fn (string $url, array $headers) => ['status' => …, 'body' => …].

It throws InvalidArgumentException for an invalid DOI and RuntimeException when the DOI can't be found.

Duplicate references

Cite::findDuplicates($refs);
// [['indexes' => [0, 4], 'reasons' => ['doi']], ['indexes' => [2, 7], 'reasons' => ['title']]]

References count as duplicates when they share a DOI, or the same title and first author. Case, accents and punctuation are ignored.

Checking a reference list

$result = Cite::checkReferences($refs, ['checkDOIs' => true]);
// ['references' => 4, 'errors' => 2, 'warnings' => 1, 'issues' => [['level' => 'error', 'code' => 'duplicate', 'ref' => 'smith2020b', ...]]]

Errors are duplicates, invalid DOIs and DOIs that can't be found (with checkDOIs). Warnings are missing titles, authors or years.

Laravel example

use Plagx\Cite\Cite;

Route::post('/cite', function (Illuminate\Http\Request $request) {
    $ref = Cite::lookupDOI($request->input('doi'));

    return [
        'apa' => Cite::formatReference($ref),
        'mla' => Cite::formatReference($ref, ['style' => 'mla']),
        'in_text' => Cite::citeInText($ref),
    ];
});

Good to know

Titles are used exactly as you give them. APA wants sentence case for article and book titles, and MLA wants title case. Plagx Cite does not change capitalisation automatically, because doing so would break names and acronyms.
The output follows the main APA 7 and MLA 9 rules for common reference types. Always check the final list against your institution's or publisher's guidelines.
For the most accurate accent handling when matching duplicates, enable the intl PHP extension (most hosts have it).

Development

composer install
composer test

Plagx Cite - Free Citation & Reference Toolkit

An open-source citation utility for students, researchers and developers. Format references, organize citations and manage bibliographies.

Developed by Plagiarism Checker X.

Plagx Cite helps with source attribution; it does not detect plagiarism or AI-generated text. For full document checks, explore Plagiarism Checker X and its AI Content Detector.

plagiarismcheckerx / plagx-cite

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