Orphadata API

Free Orphadata API with no key: Orphanet rare disease records with ICD-10 and ICD-11 mappings, OMIM and MeSH cross-references, and stated mapping relation quality.

No API key requiredCORS enabledHTTPSFree tier

Endpoint tested and returned HTTP 200 on 2026-08-21

What is the Orphadata API?

The Orphadata API is a free, key-free service publishing Orphanet's rare disease knowledge base. Cross-referencing queries return an ORPHAcode with its mappings to ICD-10, ICD-11, OMIM, MeSH, MedDRA and UMLS, each annotated with the exactness and validation status of the mapping.

Orphanet is Europe's reference resource for rare diseases, and Orphadata is its machine-readable face. The rare disease field has a specific problem this addresses: general classifications like ICD-10 simply do not have codes for most rare conditions, so mappings are approximate, contested, or absent. Orphanet's answer is to state the quality of every mapping explicitly rather than pretending it is exact.

That honesty shows in the `ExternalReference` entries. Each carries a `DisorderMappingRelation` — `E (Exact mapping: the two concepts are equivalent)` in the example — alongside a `DisorderMappingICDRelation` explaining whether the ORPHAcode has its own code in the target terminology or shares one, plus a `DisorderMappingValidationStatus`. A mapping marked narrower-than or broader-than is not wrong, but treating it as equivalence in an analysis certainly is. The response even embeds its own licence block, declaring CC BY 4.0 inline, which is a courtesy more APIs should copy.

Quick facts

Base URL: https://api.orphadata.com
Authentication: No API key or account. Orphanet data is released under CC BY 4.0, which the API states inline in a `__licence` block on every response. Attribution to Orphanet is required.
Rate limit: No published limit. Orphadata also publishes complete downloadable datasets, which suit bulk work better.
Pricing: Free. Data is CC BY 4.0 with attribution to Orphanet.
CORS: Enabled — callable directly from browser JavaScript
Official docs: Read the docs

How to use the Orphadata API

Every request below was executed against the live API on 2026-08-21, and the response shown is the real body it returned — not an illustration.

1. Fetch cross-terminology mappings for an ORPHAcode

GET https://api.orphadata.com/rd-cross-referencing/orphacodes/558?lang=en

curl

curl 'https://api.orphadata.com/rd-cross-referencing/orphacodes/558?lang=en' \
  -H 'Accept: application/json'

JavaScript (fetch)

const res = await fetch("https://api.orphadata.com/rd-cross-referencing/orphacodes/558?lang=en", {
  headers: {
    "Accept": "application/json",
  },
});
if (!res.ok) throw new Error(`Request failed: ${res.status}`);
const data = await res.json();
console.log(data);

Python (requests)

import requests

headers = {
    "Accept": "application/json",
}

res = requests.get("https://api.orphadata.com/rd-cross-referencing/orphacodes/558?lang=en", headers=headers, timeout=20)
res.raise_for_status()
print(res.json())

Response — HTTP 200 (truncated)

{
  "data": {
    "__count": 1,
    "__licence": {
      "identifier": "CC-BY-4.0",
      "link": "https://creativecommons.org/licenses/by/4.0",
      "name": "Creative Commons Attribution 4.0 International"
    },
    "results": {
      "Date": "2026-06-23 07:53:50",
      "DisorderDisorderAssociation": null,
      "DisorderFlag": [
        {
          "Label": null,
          "Value": 1
        }
      ],
      "DisorderGroup": "Disorder",
      "ExternalReference": [
        {
          "DisorderMappingICDRefUri": null,
          "DisorderMappingICDRefUrl": null,
          "DisorderMappingICDRelation": "Specific code (ICD-10/ICD-11: ORPHAcode has its own code in the targeted terminology)",
          "DisorderMappingRelation": "E (Exact mapping: the two concepts are equivalent)",
          "DisorderMappingValidationStatus": "Validated",
          "Reference": "Q87.4",
          "Source": "ICD-10"
        },
        {
          "DisorderMappingICDRefUri": 236564145,
          "DisorderMappingICDRefUrl": "https://icd.who.int/browse/latest-release/mms/en#236564145",
          "DisorderMappingICDRelation": "Specific code (ICD-10/ICD-11: ORPHAcode has its own code in the targeted terminology)",
          "DisorderMappingRelation": "E (Exact mapping: the two concepts are equivalent)",
          "DisorderMappingValidationStatus": "Validated",
          "Reference": "LD28.01",
          "Source": "ICD-11"
        },
        {
          "DisorderMappingICDRefUri": null,
          "DisorderMappingICDRefUrl": null,
          "DisorderMappingICDRelation": null,
          "DisorderMap

Parameters

Parameter	Type	Required	Description
`orphacode`	path segment	Required	The Orphanet identifier for a rare disease. `558`
`lang`	query	Optional	Language for labels: `en`, `fr`, `de`, `es`, `it`, `nl`, `pt`, `pl`. `en`
`(endpoint) /rd-cross-referencing/orphacodes/{code}`	path	Optional	Mappings to other terminologies for one disorder. `/rd-cross-referencing/orphacodes/558`
`(endpoint) /rd-classification`	path	Optional	Orphanet's own hierarchical classification of rare diseases. `/rd-classification`
`(endpoint) /rd-associated-genes`	path	Optional	Genes associated with a rare disease and the type of association. `/rd-associated-genes`
`(endpoint) /rd-phenotypes`	path	Optional	HPO phenotypes annotated to the disorder with their frequency. `/rd-phenotypes`

Response fields

data.__countinteger: Number of results in the response.
data.__licenceobject: The licence, declared inline — `CC-BY-4.0` with its identifier, name and link.
data.results.DisorderGroupstring: Whether the entry is a `Disorder`, a `Group of disorders` or a `Subtype`. This distinction drives how you should aggregate.
data.results.ExternalReference[]array: Mappings to other terminologies, one entry per target vocabulary.
ExternalReference[].Source / Referencestring: The target vocabulary and the code within it — `ICD-10` and `Q87.4` in the example.
ExternalReference[].DisorderMappingRelationstring: Exactness of the mapping, spelled out: `E (Exact mapping: the two concepts are equivalent)` and similar for narrower and broader relations.
ExternalReference[].DisorderMappingValidationStatusstring: `Validated` when curators have reviewed the mapping.
ExternalReference[].DisorderMappingICDRefUrlstring: Direct link into the WHO ICD browser for ICD-11 mappings.
data.results.Datestring: When the record was last updated in the Orphanet knowledge base.

What you can build with the Orphadata API

Map a rare disease between ORPHAcode, ICD-10, ICD-11 and OMIM
Check whether an ICD mapping is exact before using it in analysis
Build a rare disease reference with authoritative European coding
Link patient registry entries to a standard rare disease identifier
Retrieve associated genes and phenotypes for a rare condition

Common errors and how to fix them

404

Unknown ORPHAcode.

Fix: ORPHAcodes are bare integers with no prefix. Codes are occasionally retired when disorders are merged, so check the Orphanet site for a replacement.

Approximate mapping treated as exact

The relation field was ignored.

Fix: Always read `DisorderMappingRelation`. Narrower and broader mappings are common in rare disease coding and conflating them distorts any downstream count.

Empty ExternalReference

The disorder has no mappings in other terminologies.

Fix: This is genuinely common for rare diseases — most have no ICD-10 code of their own. Absence is a property of the source vocabularies, not an API failure.

Unexpected language

`lang` was omitted.

Fix: Pass `lang=en` explicitly. Orphanet is a multilingual resource and the default is not guaranteed to be English.

Orphadata API — frequently asked questions

Is the Orphadata API free?

Yes, free with no key or registration, and the data is licensed CC BY 4.0. The API helpfully declares that licence inline in a `__licence` block on every response. Attribution to Orphanet is required.

What is an ORPHAcode?

Orphanet's stable identifier for a rare disease, group of disorders or subtype. Because general classifications lack codes for most rare conditions, ORPHAcodes are often the only precise identifier a rare disease has.

Why do some diseases have no ICD-10 code?

Because ICD-10 was not designed to enumerate rare conditions, and thousands of them share a handful of residual codes or have none at all. Orphanet records that gap honestly rather than inventing a mapping, which is why the relation and validation fields matter.

Does the API cover genes and symptoms as well as codes?

Yes. Separate endpoints return associated genes with the type of gene-disease relationship, and HPO phenotype annotations with frequency information. All of it is reference data describing published knowledge, not clinical guidance.

Tools that pair with this API

JSON Formatter

Format, beautify and minify JSON online with 2-space, 4-space or tab indentation. Sort keys alphabetically and catch syntax errors instantly — free and private.

JSON Path Finder

Evaluate a dot/bracket path against your JSON and list every leaf path for discovery. Free online JSON path finder that runs 100% in your browser.

JSON to CSV Converter

Convert a JSON array of objects to CSV online. Automatic column headers from the union of all keys, delimiter choice and proper quoting — all in-browser.

Orphadata is an independent third-party service and is not affiliated with ByteTools or ByteVancer. Details on this page were verified on 2026-08-21; always check the official documentation before relying on this API in production, as terms and limits can change.