Most journal submission systems ask for a short list of keywords alongside the title and abstract, entered into their own metadata field rather than typed into the manuscript text. Those keywords do real work: they feed the controlled-vocabulary and free-text indexes that databases like PubMed/MEDLINE, Scopus, and Web of Science use to route a search query to your paper, and they populate the metadata that Google Scholar and publisher search tools crawl. Choosing them well is a distinct skill from writing a good title, even though the two fields work together — a keyword list that just repeats the title wastes an opportunity, and a keyword list built from generic or overly narrow terms fails to catch the searches a genuinely interested reader would run.
What Research Paper Keywords Actually Do
A title and abstract are read by humans and also parsed by machines, but the keyword field exists specifically for the machines: it is a discrete metadata element that indexing systems weight when matching a search query to a record, independent of whether that exact phrase appears in the title or abstract body. Because of this, keywords are most useful when they add retrieval paths the title and abstract do not already cover — synonyms a searcher might use instead of your terminology, the broader field or subfield your specific study sits within, the methodology or model system used, or a controlled-vocabulary term that a database’s own thesaurus recognizes even if you phrased the concept differently in your prose.
How Many Keywords Should You Choose
There is no single universal number: journal instructions for authors typically specify somewhere between three and eight keywords, with five or six being a common default when a journal does not give an exact figure. Some journals cap the count, some set a minimum, and a few ask for keyword phrases rather than single words. Because this varies by publisher and even by journal within the same publisher, check the specific journal’s instructions for authors before finalizing the list rather than assuming a number that worked for a previous submission — submission systems will often reject a list that is too short or too long at the technical-check stage.
Avoid Duplicating Your Title
Author guidelines at most journals discourage using keywords that simply repeat words already in the title. The reasoning is indexing efficiency: search systems already index the title itself, so a keyword field that only restates title terms adds no new retrieval surface. The more effective approach is to treat keywords as complementary to the title rather than a summary of it — use the keyword field for the synonyms, adjacent terms, methods, and broader-field descriptors a searcher might use instead of your exact title wording. See CASRAI’s companion guide on writing a discoverable research paper title for how to front-load the title itself with its own highest-value search terms, so the title and keyword field are doing complementary rather than overlapping work.
Aligning with Controlled Vocabularies: MeSH and Field-Specific Thesauri
In biomedical and health-sciences fields, many journals ask authors to draw keywords from, or align them with, Medical Subject Headings (MeSH) — the National Library of Medicine’s controlled vocabulary thesaurus used to index articles in PubMed/MEDLINE. Using recognized MeSH terms where they fit the paper’s actual content helps ensure the article surfaces correctly in MeSH-based searches and subject browsing, which many clinicians and biomedical researchers still rely on in addition to free-text search. The NLM provides a public MeSH browser for checking whether a candidate term exists as an official heading and what its accepted synonyms and narrower/broader terms are. Other fields have their own analogous controlled vocabularies maintained by the relevant indexing service (for example, Embase’s Emtree in pharmacology and clinical medicine); check whether your target journal or its primary indexing database specifies one before finalizing keywords. Outside fields with a dominant controlled vocabulary, free-text keywords chosen for how real searchers phrase queries are the norm, and controlled-vocabulary alignment is not expected.
Practical Steps to Choosing Effective Keywords
A workable process for building the list:
- Start from the paper’s core concepts — population or subject, intervention or method, and outcome or phenomenon studied — the same concepts a systematic search strategy would use, not incidental details.
- Add synonyms and alternate phrasings a searcher might use instead of your exact terminology, including both the common name and any technical or scientific name where they differ.
- Check the target journal’s controlled vocabulary (MeSH or a field-specific thesaurus) if one applies, and prefer the recognized heading over an idiosyncratic phrasing when both describe the same concept accurately.
- Cross-check against the title and abstract and cut any keyword that only restates a term already prominent in the title — replace it with a complementary term instead.
- Avoid keywords that are too broad (a whole discipline name, which returns too many unrelated results to be useful) or too narrow (a phrase so specific almost no one would search it, or one used only inside your own lab).
- Confirm the count and format against the specific journal’s instructions for authors before submission — number of keywords, whether phrases are allowed, and whether they must come from a specified thesaurus.
Common Mistakes to Avoid
The most frequent keyword-field problems are: repeating title words instead of adding complementary terms; choosing keywords that are really just the paper’s discipline or department name rather than a specific, searchable concept; ignoring a journal’s stated controlled-vocabulary requirement; and treating the keyword list as an afterthought filled in at the last minute rather than a metadata field that meaningfully affects whether the paper is found at all. Because the keyword field is entered separately from the manuscript text in most submission systems, it is easy to leave it generic or to copy a previous paper’s list without re-checking it against the current paper’s actual content — both reduce the field’s value.
Frequently Asked Questions
Can I use the same word in both the title and the keywords?
Most journal guidelines discourage keywords that only duplicate title words, since the title is already indexed separately; use the keyword field to add complementary terms — synonyms, methods, or broader/narrower concepts — instead of repeating what the title already covers.
Do all journals require MeSH terms?
No. MeSH-based keyword requirements are common in biomedical and health-sciences journals indexed in PubMed/MEDLINE, but many fields have no dominant controlled vocabulary and expect free-text keywords chosen for how researchers actually search, not terms drawn from a specific thesaurus.
Where do I check how many keywords a journal wants?
In that journal’s instructions for authors page, usually under a heading like “Keywords” or as part of the title-page/manuscript-preparation requirements; the number is not standardized across publishers.
Should keywords be single words or phrases?
Both are common; many controlled vocabularies (including MeSH) include multi-word headings, and free-text keyword fields generally accept phrases as well as single words. Follow the target journal’s own examples if it gives any.
Related CASRAI Guides
Keywords are one part of a paper’s discoverable metadata, alongside the title and abstract. See CASRAI’s guide on how to write a discoverable research paper title for the companion piece on title-level optimization, structured abstract format for how the abstract should carry related key terms, the manuscript submission process for where the keyword field is entered during submission, how major scholarly search engines index research metadata for how keywords feed into discovery platforms beyond the publisher’s own index, and the dictionary entry on the abstract for the related metadata field it sits alongside.
