Skills Taxonomy API Comparison: ESCO, O*NET, Lightcast

For a free reference taxonomy, use ESCO in Europe (13,939 skills in 28 languages), O*NET in the US, or ROME 4.0 for French job data. To turn the messy skills written in CVs and job ads into those clean entries, you need a normalization API: HireLayer, Textkernel, Lightcast, RChilli or HrFlow.ai. The two are different tools, and most products end up needing both. This guide compares the public taxonomies and the commercial APIs on size, languages, licence, price and what they actually do with free text.

HireLayer sells one of these APIs. Every other figure comes from the publisher's own site or documentation, checked on 7 October 2026, with the links at the end.

The short list

Taxonomy or API	Size	Languages	Cost and licence
ESCO	13,939 skills, 3,039 occupations	28	Free; API and downloads
O*NET	1,016 occupation titles with skills data	English	Free with registration, CC BY 4.0
ROME 4.0 (France Travail)	21,320 know-how skills, 14,301 job titles	French	Licence Ouverte 2.0, registration, 1 call a second
Lightcast Skills	33,000+ skills	English, Spanish, French	Paid licence for commercial use; free tier only for approved public-good projects
HireLayer Skills	11,061 skills with families and domains	French and English	1 credit per call, from €0.0445; 50 free a month
Textkernel Skills Intelligence	12,000+ skills, 4,500+ professions	25 for skills	0.1 credit per item normalized; plans from $99 a month
RChilli Taxonomy	3M+ skills (vendor figure)	Multiple	0.3 credit per search
HrFlow.ai Tagging	5,000-label skills tagger, plus ESCO, O*NET and ROME taggers	43+	Not published

Taxonomy or normalization API?

A skills taxonomy is a reference list: each skill has an id, a preferred name, synonyms and links to broader skills or occupations. ESCO, O*NET and ROME are taxonomies. Their APIs let you look up or search entries, but they do not read a CV for you.

A normalization API takes free text, such as "Pack Office (Word, Excel)" or a whole skills section, and returns the matching taxonomy entries with their ids. That is the step that lets you compare a candidate's "JS, React.js" with a job that asks for "JavaScript, React". Without it, search and matching run on strings, and strings rarely agree.

So the usual setup is a taxonomy you trust, plus an API that maps text onto it. Some vendors ship their own taxonomy and the mapping togehter; others, like HrFlow.ai, tag text against public taxonomies.

Public taxonomies

ESCO

ESCO is the European Commission's classification of skills, competences and occupations. Version 1.2.1 lists 13,939 skills and 3,039 occupations in 28 languages, which makes it the default choice for multilingual European products. It is free to consult and download in formats from CSV to JSON-LD, and the web service API answered our test query without a key. The API searches and looks up entries; it does not extract skills from text.

O*NET

O*NET, run for the US Department of Labor, describes 1,016 occupations with the skills, knowledge and abilities each one requires. The data is under CC BY 4.0 and the web services are free after registration, with attribution. It is the reference for US occupations, but its skills model is broad (around job requirements) rather than a long list of tools and technologies.

ROME 4.0

France Travail's ROME is the reference for the French labour market: 21,320 know-how skills in a five-level tree, 17,319 knowledge items and 14,301 job titles, under the Licence Ouverte 2.0. The APIs are open after registration on francetravail.io, limited to one call per second. If you build for French employers or job boards, it is the taxonomy your users will recognise.

Normalization APIs

HireLayer Skills

HireLayer Skills resolves free text in French or English, from one skill to a whole CV section of up to 5,000 characters, to a taxonomy of 11,061 skills. Each result has a stable id, a type (hard skill, software, certification, soft skill or language), its families and domains, and, when there is one, a broader skill to widen a search (Excel to Microsoft Office). Text that matches nothing comes back in an unresolved list with likely families, rather than a guess. One call costs one credit whatever the length of the text, and you can download the whole taxonomy with GET /api/v1/skills.

Best for: French and English products that want text in and stable ids out, with a published price.

Textkernel Skills Intelligence

Textkernel offers skills extraction, normalization, autocomplete and an ontology to compare skills and professions: over 12,000 skills with 300,000 synonyms in 25 languages, and 4,500 professions mapped to ISCO and O*NET. Normalizing costs 0.1 credit per input item and extracting from text 0.1 credit plus 0.04 per 1,000 characters. Licensing the full taxonomy structure goes through an account manager.

Best for: multilingual products that need skills and professions in one ontology.

Lightcast

Lightcast's skills taxonomy (formerly Open Skills) has more than 33,000 skills in a skill, subcategory and category hierarchy, with an extraction endpoint. The taxonomy is free to browse, but using the API commercially needs a paid licence with no public price. Free access exists for approved nonprofit and public-good projects, capped at 50 extraction calls a month. The CC BY-SA licence people often quote applies only to the Wikipedia descriptions, not to the taxonomy itself.

Best for: labour-market analytics and teams that already license Lightcast data.

RChilli

RChilli exposes skill, job and keyword search over a taxonomy it describes as 3 million skills and 2.4 million job profiles, at 0.3 credit per call, plus an autocomplete add-on at $500 a month. It also offers taxonomy lookups in O*NET and ESCO through its MCP server.

HrFlow.ai

HrFlow.ai's Tagging API returns the top tags for a text with likelihood scores, using its own 5,000-label skills tagger or standard taggers for ESCO, O*NET and ROME, and a Taxonomy API lets you maintain your own. It claims more than 43 languages. Prices are not published.

JANZZ and SharpAPI

JANZZ.technology sells an occupation and skills ontology (JANZZon!) mapped to ISCO-08, O*NET and ESCO, with a start-up licence example at $1,500 a month. SharpAPI has a skills database API with word-based plans from $50 a month; its own pages give two diffrent sizes for the database (73,000+ and nearly 100,000 skills), so check it on your own data.

How to choose

Start from your market. ESCO for multilingual Europe, ROME for France, O*NET for US occupations.
Test normalization on your own text. Take 200 skills copied from real CVs and job ads, with typos, abbreviations and mixed languages, and count how many come back with the right id. Size of the taxonomy matters less than this hit rate.
Check what happens to unknown skills. An API that guesses the nearest skill pollutes your data; one that flags the text as unresolved lets you review it.
Read the licence twice. "Free to browse" and "free to use in a commercial product" are not the same.
Store ids, not names. Names get renamed and translated; stable ids keep your search and matching consistant over time.

The HireLayer Skills API page shows a full request and response, and the Skills reference lists every field. To use normalized skills for scoring, see our candidate matching API comparison.

Try the live demo Read the API documentation View pricing

Frequently asked questions

What is a skills taxonomy?

A structured list of skills, each with an id, a preferred name, synonyms and relations to broader skills or occupations. ESCO, O*NET, ROME and Lightcast are examples.

Is there a free skills taxonomy API?

Yes. ESCO's API and downloads are free, O*NET web services are free with registration and attribution, and France Travail's ROME 4.0 APIs are open under the Licence Ouverte. Lightcast's free tier is limited to approved public-good projects.

How many skills does ESCO have?

ESCO v1.2.1 lists 13,939 skills and 3,039 occupations, in 28 languages.

What is skills normalization?

Mapping the free text people write, such as "MS Excel" or "Pack Office", to standard skills with stable ids, so that a candidate and a job that describe the same skill differently can be compared.

Can I use ESCO and a normalization API together?

Yes, and it is common: keep ESCO or ROME as the shared reference for reporting, and use an API to map raw text from CVs and job ads to skills. Some APIs, such as HrFlow.ai's taggers, return ESCO, O*NET or ROME entries directly.

Sources and further reading

Louis Desclous

Published on October 7, 2026 · Reading time: 8 minutes