Query the Ensembl REST API for gene/transcript/protein lookup, sequence retrieval, comparative genomics (Compara), variant effect prediction (VEP), regulatory features, and cross-species ortholog/paralog calls. Use when pulling Ensembl-native data (Ensembl Gene IDs, version-pinned releases, archive endpoints for reproducibility), gene/transcript/exon structure with stable IDs, or VEP for variant annotation. Encodes the 15 req/sec rate limit, archive (e110.rest.ensembl.org) for reproducibility, Ensembl divisions (vertebrates / plants / fungi / metazoa / bacteria), and the symbol-vs-ID stability problem.
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Query the Ensembl REST API for gene/transcript/protein lookup, sequence retrieval, comparative genomics (Compara), variant effect prediction (VEP), regulatory features, and cross-species ortholog/paralog calls. Use when pulling Ensembl-native data (Ensembl Gene IDs, version-pinned releases, archive endpoints for reproducibility), gene/transcript/exon structure with stable IDs, or VEP for variant annotation. Encodes the 15 req/sec rate limit, archive (e110.rest.ensembl.org) for reproducibility, Ensembl divisions (vertebrates / plants / fungi / metazoa / bacteria), and the symbol-vs-ID stability problem.
tool_type
python
primary_tool
requests
Version Compatibility
Reference examples tested with: requests 2.31+, Ensembl REST API (release 110+); Ensembl release schedule is roughly quarterly
Before using code patterns, verify installed versions match. If versions differ:
Each Ensembl release has an archive REST endpoint (e.g. https://e110.rest.ensembl.org) for reproducibility.
Ensembl REST
"Pull Ensembl-native gene / transcript / variant data programmatically" -> Ensembl REST is distinct from NCBI Entrez and BioMart. It is the right answer for: stable Ensembl IDs, transcript / exon structure, VEP (Variant Effect Predictor) annotation, Compara orthologs at vertebrate scale, regulatory feature annotation, and any workflow rooted in Ensembl's coordinate system.
Two facts dominate Ensembl REST work: (1) the 15 req/sec / 55,000 req/hour rate limit — high enough for hundreds of queries, low enough that bulk work (>5,000) belongs in BioMart instead; (2) versioned archive endpoints — https://e110.rest.ensembl.org pins to release 110 for reproducibility, while https://rest.ensembl.org follows the current release.
For non-vertebrate work, check ensemblgenomes.org mirrors. As of 2024, Ensembl Genomes was being consolidated; check current host.
Version pinning
URL
Behavior
https://rest.ensembl.org
Current release (rolling)
https://e110.rest.ensembl.org
Pinned to release 110
https://e111.rest.ensembl.org
Pinned to release 111
https://grch37.rest.ensembl.org
Pinned to GRCh37 (legacy assembly)
For any published analysis, pin the release. Ensembl releases change gene model versions, exon coordinates, and transcript annotations — re-running a pipeline a year later against the live endpoint may produce different results.
Gene symbols are unstable (MARCH1 -> MARCHF1 in 2020 due to Excel autocorrect; SEPT* family also renamed). Ensembl Gene IDs (ENSG...) are stable across releases when the gene model is preserved.
Best practice:
Resolve symbol -> Ensembl ID once at pipeline start: /lookup/symbol/{species}/{symbol}.
Persist the Ensembl ID.
Run downstream queries by ID, not symbol.
Symbol-based endpoints are convenient for interactive use; ID-based endpoints are for reproducible pipelines.
Rate-limit math
Limit
Value
Burst
15 req/sec
Hourly
55,000 req/hour
Concurrent
Not enforced; courtesy 1-2
Respect Retry-After header on HTTP 429. For >5,000 queries, switch to BioMart bulk export (see biomart-queries) — BioMart has separate, more permissive limits.
VEP (Variant Effect Predictor)
VEP via REST is the right call for ad hoc variant annotation. For batch variant annotation (>1000 variants), download VEP and run locally (variant-calling/variant-annotation skill).
REST modes:
/vep/{species}/region/{region}/{allele} — single variant by coordinate
/vep/{species}/id/{variant_id} — by dbSNP / Ensembl variant ID
/vep/{species}/hgvs/{hgvs_notation} — by HGVS notation
defgenes_in_region(species, region):
'''region as "chr:start-end" e.g. "17:43000000-44000000".'''
r = get_with_retry(f'{BASE}/overlap/region/{species}/{region}',
params={'feature': 'gene'})
return r.json()
for g in genes_in_region('human', '17:43000000-43200000'):
print(f' {g["external_name"]:<12}{g["id"]}{g["biotype"]:<20}{g["start"]}-{g["end"]}')
VEP for a single variant
Goal: Get full annotation for a variant by coordinate.
defvep_region(species, region, allele):
r = get_with_retry(f'{BASE}/vep/{species}/region/{region}/{allele}')
return r.json()
# BRCA1 missense variant in GRCh38 coordinates (rest.ensembl.org defaults to GRCh38);# for GRCh37 coords use https://grch37.rest.ensembl.org instead.
results = vep_region('human', '17:43044295-43044295:1', 'A')
if results:
for tc in results[0].get('transcript_consequences', [])[:5]:
print(f' {tc["gene_symbol"]:<8}{tc["consequence_terms"]}')
if'sift_prediction'in tc:
print(f' SIFT: {tc["sift_prediction"]} ({tc.get("sift_score", "?")})')
Compara orthologs (Compara via REST)
deforthologs(species, symbol, target_species=None):
params = {'type': 'orthologues'}
if target_species:
params['target_species'] = target_species
r = get_with_retry(f'{BASE}/homology/symbol/{species}/{symbol}', params=params)
return r.json()['data'][0]['homologies']
for o in orthologs('human', 'BRCA1', target_species='mouse'):
print(f' {o["target"]["species"]:<15}{o["target"]["id"]} type={o["type"]} confidence={o.get("confidence")}')
Batch lookup with rate-limit handling
defbatch_symbols(species, symbols):
out = {}
for sym in symbols:
try:
out[sym] = symbol_to_ensembl(species, sym)
except requests.HTTPError as e:
out[sym] = {'error': str(e)}
time.sleep(0.07) # 15 req/sec ceilingreturn out
Archive endpoint for reproducibility
# Pin to release 110
ARCHIVE = 'https://e110.rest.ensembl.org'
r = requests.get(f'{ARCHIVE}/lookup/symbol/human/BRCA1', headers={'Accept': 'application/json'})
print(r.json()['id'])
# Re-runs against e110 in 2030 will return the same Gene ID even if the live release has moved on.
