loc-catalog

name	loc-catalog
description	Search the Library of Congress digital collections via the loc.gov JSON API. Use this skill whenever the user wants to search LOC's digitized books, photos, maps, manuscripts, newspapers, audio, or film/video, look up items by LCCN, browse LOC collections, find primary sources with date range filters, or retrieve citations and download links for LOC materials. Also triggers when cross-referencing items found in other library catalogs against LOC holdings.
version	1.0.0

Library of Congress API Skill

Search and retrieve items from LOC's digitized collections — books, photos, maps, manuscripts, newspapers, audio, and more.

Critical: Things Claude Won't Know Without This Skill

This API covers digitized collections, NOT the full library catalog

The loc.gov JSON API searches LOC's digitized and online collections — not the full OPAC. By default, only digitized items are returned. Add all=true to include non-digitized catalog records.

JSON requires fo=json parameter, NOT a URL extension

Unlike LibraryCloud (.json extension), LOC uses a query parameter:

CORRECT: https://www.loc.gov/search/?q=hamlet&fo=json
WRONG:   https://www.loc.gov/search.json?q=hamlet

Facet filters use fa= with pipe separators

Single:   ?fa=subject:physics
Multiple: ?fa=subject:wildlife|location:yellowstone

Available facet fields: subject, contributor, location, language, original-format, online-format, partof, digitized, access-restricted.

Format-specific endpoints are shortcuts

/books/, /photos/, /maps/, /audio/, /newspapers/, /manuscripts/, /film-and-videos/, /notated-music/ all accept the same params as /search/.

Key Search Parameters

Param	Description	Example
q	Keyword search	q=hamlet+shakespeare
fa	Facet filter	fa=subject:physics|language:english
dates	Date range (YYYY/YYYY)	dates=1920/1940
c	Results per page (25, 50, 100, 150)	c=50
sp	Page number (starts at 1)	sp=2
sb	Sort: date, date_desc, title_s, title_s_desc	sb=date_desc
all	Include non-digitized (true/false)	all=true
at	Select attributes (comma-sep)	at=item,resources
fo	Format: json or yaml	fo=json

Item Lookup by LCCN/ID

https://www.loc.gov/item/{LCCN}/?fo=json

Returns full item detail including cite_this (APA/Chicago/MLA citations), resources (download links), other_formats (MARCXML, MODS, Dublin Core).

Response Structure

Search Results

{
  "results": [
    {
      "id": "http://www.loc.gov/item/95521789/",
      "title": "Item title",
      "date": "1796-01-01",
      "contributor": ["Name"],
      "subject": ["Subject term"],
      "language": ["English"],
      "original_format": ["book"],
      "description": ["..."],
      "image_url": ["//tile.loc.gov/..."],
      "digitized": true,
      "number_lccn": ["95521789"]
    }
  ],
  "pagination": {
    "of": 85604,
    "total": 17121,
    "perpage": 5,
    "current": 1
  },
  "facets": { ... }
}

Item Detail

The item object adds: call_number, created_published, rights, summary, stmt_of_responsibility, genre, and cite_this with pre-formatted citations.

Python Script

from scripts.loc_api import LocAPI
loc = LocAPI()

# Keyword search
results = loc.search("hamlet shakespeare", limit=10)

# Format-specific
photos = loc.search("civil war", format="photos", dates="1860/1865")

# Faceted search
results = loc.search("wildlife", facets={"subject": "birds", "location": "yellowstone"})

# Item lookup
item = loc.get_item("95521789")
citation = loc.get_citation(item, style="apa")

# Browse collections
collections = loc.list_collections()
items = loc.browse_collection("civil-war-maps", limit=20)

# Summarize
for r in results[:5]:
    print(loc.summarize(r))

Pagination

• Max 150 results per page (c=150)
• Hard limit: cannot paginate past 100,000th result
• Use facets/date ranges to narrow large result sets

API Etiquette

• No authentication required
• Rate limiting is enforced (exact limits unpublished) — add 0.5-1s between requests
• Include a User-Agent header

Related Skills

• harvard-library-catalog: Cross-reference Harvard holdings with LOC items
• hathitrust-catalog: Use LCCNs from LOC to check HathiTrust for digital full-text
• wikidata-search: LOC authority IDs (P244) link Wikidata entities to LOC records

Resources

• references/api_reference.md — Complete parameter and response field reference
• scripts/loc_api.py — Python client with search, item lookup, collection browsing, and citation extraction