Lexicon vs MeSH vs UMLS

Feature	MeSH (NLM)	UMLS	Lexicon API
Controlled vocabulary	Yes	Yes	Yes + auto-expanding
REST API	Limited (E-Utils)	SOAP/REST (complex)	Simple REST + JSON
Emerging terms	No (annual updates)	No	Real-time discovery
Auto-learn from queries	No	No	Yes (MeSH + PubMed lookup)
Beyond-MeSH detection	N/A	N/A	Watchtower-powered
PICO terminology	Partial	Partial	Native PICO category
Methodology terms	No	Partial	Built-in (ROB2, PRISMA, etc.)
Batch lookup	No	Limited	Up to 100 terms/request
Free tier	Yes	Yes (license required)	Yes (100 req/day)
Setup complexity	Medium	High (UMLS license)	1 header, instant

Pricing

Free

$0

100 requests/day
search + lookup + stats
JSON responses
learn endpoint
batch lookup

Get Free Key

Popular

Developer

$29/mo

10,000 requests/day
All endpoints
learn (auto-discover)
beyond_mesh access
batch lookup

Subscribe

Enterprise

$99/mo

Unlimited requests
All endpoints
batch (100 terms/req)
Priority support
SLA 99.9%

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API Documentation

Base URL: https://evidenx.lat/api/lexicon-api.php

Authentication: Pass your key via X-API-Key header or ?key= query parameter.

GET ?action=search&q={query}

Fuzzy search across all approved terms. Returns matching terms with definitions.

Params: q (required, min 2 chars), limit (optional, max 50)

curl "https://evidenx.lat/api/lexicon-api.php?action=search&q=cardiac+remodeling" \
  -H "X-API-Key: lex_your_key_here"

{
  "ok": true,
  "query": "cardiac remodeling",
  "count": 2,
  "terms": [
    {
      "term": "Cardiac Remodeling",
      "definition": "Adaptive structural and functional changes...",
      "category": "mesh",
      "mesh_id": "D020257",
      "usage_count": 15
    }
  ]
}

GET ?action=lookup&term={exact_term}

Exact lookup with full data including aliases and MeSH ID.

curl "https://evidenx.lat/api/lexicon-api.php?action=lookup&term=exercise-induced+arrhythmia" \
  -H "X-API-Key: lex_your_key_here"

GET ?action=beyond_mesh

Terms discovered by Watchtower that are NOT in MeSH vocabulary. The unique value of this API.

curl "https://evidenx.lat/api/lexicon-api.php?action=beyond_mesh&limit=20" \
  -H "X-API-Key: lex_your_key_here"

POST action=learn

Auto-discover a term. Searches MeSH and PubMed, creates definition, adds to Lexicon. Developer+ only.

curl -X POST "https://evidenx.lat/api/lexicon-api.php" \
  -H "X-API-Key: lex_your_key_here" \
  -H "Content-Type: application/json" \
  -d '{"action":"learn","term":"exercise-induced cardiac fatigue"}'

{
  "ok": true,
  "action": "learned",
  "category": "mesh_x",
  "mesh_id": null,
  "definition": "Found in 847 PubMed articles."
}

POST action=batch

Batch lookup up to 100 terms in one request. Enterprise only.

curl -X POST "https://evidenx.lat/api/lexicon-api.php" \
  -H "X-API-Key: lex_your_key_here" \
  -H "Content-Type: application/json" \
  -d '{"action":"batch","terms":["ARDS","low tidal volume","PEEP"]}'

Rate Limit Headers

Every response includes:

X-RateLimit-Limit: 10000
X-RateLimit-Remaining: 9847
X-RateLimit-Reset: 1712534400
X-Lexicon-Plan: developer

Use Cases

NLP Pipelines

Enrich your NLP models with validated scientific terminology. Use beyond_mesh to catch terms your pipeline misses.

Systematic Review Tools

Auto-validate PICO terms, expand search strategies with MeSH synonyms, detect emerging terminology in your field.

Research Dashboards

Feed your dashboards with real-time terminology intelligence. Track which terms are emerging vs. established.

Clinical Research Intelligence APIReal-time semantic layer that anticipates what MeSH will index next.