PubChem API

Base URL

https://pubchem.ncbi.nlm.nih.gov/rest/pug

Authentication

No API key required.

Rate limit

5 requests per second and 400 per minute per IP.

Pricing

Free public domain US government data.

CORS

Enabled — callable directly from browser JavaScript

Official docs

Read the docs

Every request below was executed against the live API on 20 Aug 2026, and the response shown is the real body it returned — not an illustration.

curl 'https://pubchem.ncbi.nlm.nih.gov/rest/pug/compound/name/aspirin/property/MolecularFormula,MolecularWeight/JSON'

const res = await fetch("https://pubchem.ncbi.nlm.nih.gov/rest/pug/compound/name/aspirin/property/MolecularFormula,MolecularWeight/JSON");
if (!res.ok) throw new Error(`Request failed: ${res.status}`);
const data = await res.json();
console.log(data);

import requests

res = requests.get("https://pubchem.ncbi.nlm.nih.gov/rest/pug/compound/name/aspirin/property/MolecularFormula,MolecularWeight/JSON", timeout=20)
res.raise_for_status()
print(res.json())

{
  "PropertyTable": {
    "Properties": [
      {
        "CID": 2244,
        "MolecularFormula": "C9H8O4",
        "MolecularWeight": "180.16"
      }
    ]
  }
}

PropertyTable.Propertiesarray

One entry per matched compound.

...CIDinteger

PubChem Compound ID — the canonical identifier.

...MolecularFormulastring

Chemical formula, e.g. C9H8O4.

...MolecularWeightstring

Molecular weight, returned as a string.

...CanonicalSMILESstring

SMILES structure notation, when requested.

...IUPACNamestring

Systematic IUPAC name, when requested.

• Build a chemical compound lookup for education or research
• Convert between chemical names, formulas and structures
• Enrich a drug database with molecular properties
• Validate chemical identifiers in a laboratory system

If PubChem does not fit, these health & medical apis cover similar ground. Every one was called before publishing, and each links to its own reference page with a working curl command and the response it returned.