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OpenAlex API Complete Guide

Base Information

Base URL: https://api.openalex.org Authentication: None required Rate Limits:

• Default: 1 request/second, 100k requests/day
• Polite pool (with email): 10 requests/second, 100k requests/day

Critical Best Practices

✅ DO: Use ?sample parameter for random sampling

https://api.openalex.org/works?sample=20&seed=123

For large samples (10k+), use multiple seeds and deduplicate.

❌ DON'T: Use random page numbers for sampling

Incorrect: ?page=5, ?page=17 - This biases results!

✅ DO: Use two-step lookup for entity filtering

1. Find entity ID: /authors?search=einstein
2. Use ID: /works?filter=authorships.author.id:A5023888391

❌ DON'T: Filter by entity names directly

Incorrect: /works?filter=author_name:Einstein - Names are ambiguous!

✅ DO: Use maximum page size for bulk extraction

?per-page=200

This is 8x faster than default (25).

❌ DON'T: Use default page sizes

Default is only 25 results per page.

✅ DO: Use OR filter (pipe |) for batch lookups

/works?filter=doi:10.1/abc|10.2/def|10.3/ghi

Up to 50 values per filter.

❌ DON'T: Make sequential API calls for lists

Making 100 separate calls when you can batch them is inefficient.

✅ DO: Implement exponential backoff for retries

for attempt in range(max_retries):
    try:
        response = requests.get(url)
        if response.status_code == 200:
            return response.json()
    except:
        wait_time = 2 ** attempt
        time.sleep(wait_time)

✅ DO: Add email for 10x rate limit boost

?mailto=yourname@example.edu

Increases from 1 req/sec → 10 req/sec.

Entity Endpoints

• /works - 240M+ scholarly documents
• /authors - Researcher profiles
• /sources - Journals, repositories, conferences
• /institutions - Universities, research organizations
• /topics - Subject classifications (3-level hierarchy)
• /publishers - Publishing organizations
• /funders - Funding agencies
• /text - Tag your own text with topics/keywords (POST)

Essential Query Parameters

Filter Syntax

Basic Filtering

Single filter:     ?filter=publication_year:2020
Multiple (AND):    ?filter=publication_year:2020,is_oa:true
Values (OR):       ?filter=type:journal-article|book
Negation:          ?filter=type:!journal-article

Comparison Operators

Greater than:      ?filter=cited_by_count:>100
Less than:         ?filter=publication_year:<2020
Range:             ?filter=publication_year:2020-2023

Multiple Values in Same Attribute

Repeat filter:     ?filter=institutions.country_code:us,institutions.country_code:gb
Use + symbol:      ?filter=institutions.country_code:us+gb

Both mean: "works with author from US AND author from GB"

OR Queries

Any of these:      ?filter=institutions.country_code:us|gb|ca
Batch IDs:         ?filter=doi:10.1/abc|10.2/def

Up to 50 values with pipes.

Common Query Patterns

Get Random Sample

# Small sample
https://api.openalex.org/works?sample=20&seed=42

# Large sample (10k+) - make multiple requests
https://api.openalex.org/works?sample=1000&seed=1
https://api.openalex.org/works?sample=1000&seed=2
# Then deduplicate by ID

Search Works

# Simple search
https://api.openalex.org/works?search=machine+learning

# Search specific field
https://api.openalex.org/works?filter=title.search:CRISPR

# Search + filter
https://api.openalex.org/works?search=climate&filter=publication_year:2023

Find Works by Author (Two-Step)

# Step 1: Get author ID
https://api.openalex.org/authors?search=Heather+Piwowar
# Returns: "id": "https://openalex.org/A5023888391"

# Step 2: Get their works
https://api.openalex.org/works?filter=authorships.author.id:A5023888391

Find Works by Institution (Two-Step)

# Step 1: Get institution ID
https://api.openalex.org/institutions?search=MIT
# Returns: "id": "https://openalex.org/I136199984"

# Step 2: Get their works
https://api.openalex.org/works?filter=authorships.institutions.id:I136199984

Highly Cited Recent Papers

https://api.openalex.org/works?filter=publication_year:>2020&sort=cited_by_count:desc&per-page=200

Open Access Works

# All OA
https://api.openalex.org/works?filter=is_oa:true

# Gold OA only
https://api.openalex.org/works?filter=open_access.oa_status:gold

Multiple Criteria

# Recent OA works about COVID from top institutions
https://api.openalex.org/works?filter=publication_year:2022,is_oa:true,title.search:covid,authorships.institutions.id:I136199984|I27837315

Bulk DOI Lookup

# Get specific works by DOI (up to 50 per request)
https://api.openalex.org/works?filter=doi:https://doi.org/10.1371/journal.pone.0266781|https://doi.org/10.1371/journal.pone.0267149&per-page=50

Aggregate Data

# Top topics
https://api.openalex.org/works?group_by=topics.id

# Papers per year
https://api.openalex.org/works?group_by=publication_year

# Most prolific institutions
https://api.openalex.org/works?group_by=authorships.institutions.id

Pagination

# First page
https://api.openalex.org/works?filter=publication_year:2023&per-page=200

# Next pages
https://api.openalex.org/works?filter=publication_year:2023&per-page=200&page=2

Response Structure

List Endpoints

{
  "meta": {
    "count": 240523418,
    "db_response_time_ms": 42,
    "page": 1,
    "per_page": 25
  },
  "results": [
    { /* entity object */ }
  ]
}

Single Entity

https://api.openalex.org/works/W2741809807
→ Returns Work object directly (no meta/results wrapper)

Group By

{
  "meta": { "count": 100 },
  "group_by": [
    {
      "key": "https://openalex.org/T10001",
      "key_display_name": "Artificial Intelligence",
      "count": 15234
    }
  ]
}

Works Filters (Most Common)

Authors Filters

External ID Support

Works

DOI:  /works/https://doi.org/10.7717/peerj.4375
PMID: /works/pmid:29844763

Authors

ORCID: /authors/https://orcid.org/0000-0003-1613-5981

Institutions

ROR: /institutions/https://ror.org/02y3ad647

Sources

ISSN: /sources/issn:0028-0836

Performance Tips

1. Use maximum page size: ?per-page=200 (8x fewer calls)
2. Batch ID lookups: Use pipe operator for up to 50 IDs
3. Select only needed fields: ?select=id,title,publication_year
4. Use concurrent requests: With rate limiting (10 req/sec with email)
5. Add email: ?mailto=you@example.edu for 10x speed boost

Error Handling

HTTP Status Codes

• 200 - Success
• 400 - Bad request (check filter syntax)
• 403 - Rate limit exceeded (implement backoff)
• 404 - Entity doesn't exist
• 500 - Server error (retry with backoff)

Exponential Backoff

def fetch_with_retry(url, max_retries=5):
    for attempt in range(max_retries):
        try:
            response = requests.get(url, timeout=30)
            if response.status_code == 200:
                return response.json()
            elif response.status_code in [403, 500, 502, 503, 504]:
                wait_time = 2 ** attempt
                time.sleep(wait_time)
            else:
                response.raise_for_status()
        except requests.exceptions.Timeout:
            if attempt < max_retries - 1:
                time.sleep(2 ** attempt)
            else:
                raise
    raise Exception(f"Failed after {max_retries} retries")

Rate Limiting

Without Email (Default Pool)

• 1 request/second
• 100,000 requests/day

With Email (Polite Pool)

• 10 requests/second
• 100,000 requests/day
• Always use for production

Concurrent Request Strategy

1. Track requests per second globally
2. Use semaphore or rate limiter across threads
3. Monitor for 403 responses
4. Back off if limits hit

Common Mistakes to Avoid

1. ❌ Using page numbers for sampling → ✅ Use ?sample=
2. ❌ Filtering by entity names → ✅ Get IDs first
3. ❌ Default page size → ✅ Use per-page=200
4. ❌ Sequential ID lookups → ✅ Batch with pipe operator
5. ❌ No error handling → ✅ Implement retry with backoff
6. ❌ Ignoring rate limits → ✅ Global rate limiting
7. ❌ Not including email → ✅ Add mailto=
8. ❌ Fetching all fields → ✅ Use select=

Additional Resources

• Full documentation: https://docs.openalex.org
• API Overview: https://docs.openalex.org/how-to-use-the-api/api-overview
• Entity schemas: https://docs.openalex.org/api-entities
• Help: https://openalex.org/help
• User group: https://groups.google.com/g/openalex-users