libofcongress-mcp-server

<div align="center"> <h1>@cyanheads/libofcongress-mcp-server</h1> <p><b>Search LOC digital collections, browse Chronicling America newspapers with full OCR text, and look up LC Subject Headings via MCP. STDIO or Streamable HTTP.</b> <div>6 Tools • 1 Resource</div> </p> </div> <div align="center">

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Public Hosted Server: https://libofcongress.caseyjhand.com/mcp

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Tools

Six tools covering the Library of Congress digital holdings — general search with format/date/subject/location filters, full item retrieval, Chronicling America newspaper search with OCR, single-page full-text fetch, LCSH subject heading lookup, and curated collection browsing:

| Tool | Description | |:-----|:------------| | libofcongress_search | Search LOC digital collections by keyword with optional format, date range, subject heading, geographic location, and collection filters. Returns item summaries with IDs for follow-up retrieval. | | libofcongress_get_item | Retrieve full metadata for a specific LOC item — contributors, subjects, summary, languages, locations, rights, physical description, call number, formats, access restrictions, resource links (TIFF/JPEG/PDF), and related items. | | libofcongress_search_newspapers | Search historical newspaper pages in the Chronicling America corpus. Returns pages with OCR text excerpts (~500 chars), publication title, date, state, and the URL needed for libofcongress_get_newspaper_page. | | libofcongress_get_newspaper_page | Retrieve the full OCR text of a specific newspaper page. Pass the url field from a libofcongress_search_newspapers result. Returns ocr_available: false when the page has no digitized text. | | libofcongress_search_subjects | Search Library of Congress Subject Headings (LCSH) by keyword. Returns controlled-vocabulary labels and URIs — use the label as the subject filter in libofcongress_search. | | libofcongress_browse_collections | List and browse LOC curated digital collections with descriptions, item counts, and slugs. Optionally filter by keyword. |

libofcongress_search

Search the LOC digital collections with full-text keyword matching and facet filters.

• Eight material formats: photo, map, newspaper, manuscript, audio, film, book, notated-music
• Date range filtering by year (inclusive start and end)
• Subject heading filter — use libofcongress_search_subjects first to get the exact LCSH spelling
• Geographic location filter (e.g., "oklahoma", "washington d.c.")
• collection_slug scopes the search to one curated collection — pass a slug from libofcongress_browse_collections. Mutually exclusive with format (each selects a different LOC endpoint); an unknown slug returns collection_not_found
• Pagination up to 100 results per page — pages/has_next respect LOC's ~100,000-item retrieval ceiling (a notice discloses how to reach the rest: partition by date, subject, or location); real results on a page beyond the reported total are always returned, never discarded
• Empty results include a notice field with recovery hints — echoes the applied filters
• Each result carries is_item — true for catalog items whose id resolves via libofcongress_get_item, false for non-item results (collections, exhibit/guide pages, newspaper pages); open their url instead

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libofcongress_get_item

Retrieve the full metadata record for a specific LOC digital item.

• Returns contributors, LCSH subject headings, rights information, physical/technical description, and cataloger notes
• Also returns summary, languages, locations, call_number (shelf location for requesting the physical original), former_ids, original_formats, online_formats, and access_restricted — all sourced from the same upstream response, no extra request
• resource_links contains URLs to downloadable digital files (TIFF, JPEG, PDF) for items with digital surrogates
• related_items lists IDs of related LOC items for follow-up retrieval
• resource_links and related_items render in full in both structuredContent and content[] — no truncation, so content[]-only clients see every value
• Deduplicates resource links from nested files[] arrays
• Accepts multi-segment item IDs verbatim (e.g. newspaper pages sn95047246/1935-09-05/ed-1); returned url is always an absolute https:// URL
• Fields absent upstream are omitted rather than filled — a sparse record stays sparse

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libofcongress_search_newspapers

Search historical newspaper pages in the Chronicling America corpus via the LOC /newspapers/ endpoint.

• OCR text excerpts (~500 chars) returned inline for relevance assessment without a second hop
• Filters: keyword, date range, US state (full state name), newspaper publication title (partial match)
• Returns the url field needed by libofcongress_get_newspaper_page — do not construct these URLs manually
• OCR quality varies by digitization batch and era; 19th-century and degraded materials may contain garbled text
• Empty results include a notice with recovery suggestions (broaden date, try different keywords, historical OCR caveat)

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libofcongress_get_newspaper_page

Retrieve the full OCR text and metadata for a specific newspaper page.

• Accepts the url field from a libofcongress_search_newspapers result — validates the URL prefix before any outbound request
• Fetches JSON from the LOC text-services endpoint (tile.loc.gov) and reads plain text from the full_text field
• ocr_available: false when the page has no digitized text (image-only batch) — not an error, a data property
• When ocr_available is true but the text service returns nothing, a notice discloses the retrieval miss on both response surfaces — distinct from a genuinely image-only page
• Strips echoed q= params from fulltext URLs to avoid tile.loc.gov 404s (known LOC API quirk)

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libofcongress_search_subjects

Search Library of Congress Subject Headings (LCSH) via id.loc.gov.

• Returns standardized labels and stable LOC URIs for subjects matching the keyword
• count field indicates approximate number of LOC items carrying that heading (when available)
• Use the returned label exactly in the libofcongress_search subject filter — LCSH uses inverted forms ("Photography, Aerial", "World War, 1939-1945") that differ from natural language
• Draws from the id.loc.gov suggest endpoint's full 50-candidate pool (not scaled to limit) and filters to true LCSH headings, so a heading ranked below name-authority records isn't reported as a false empty; when that ranked pool — rather than a lack of coverage — yields an empty or short result, the response discloses it with a recovery hint

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libofcongress_browse_collections

List and browse LOC curated digital collections.

• Returns collection slug — pass it to libofcongress_search as collection_slug to search inside that collection
• Slugs come from the collection's loc.gov route, not its title — "Aaron Copland Collection" lives at aaron-copland, so they aren't guessable
• Optional keyword filter by collection name/description
• Item counts are approximate; omitted when the API doesn't provide them
• Pagination supported up to 100 collections per page

Resource

| Type | Name | Description | |:-----|:-----|:------------| | Resource | libofcongress://item/{+item_id} | LOC digital item metadata by ID. Stable URI for injecting item context into agent conversations. Returns the same full record as libofcongress_get_item. |

All resource data is also reachable via libofcongress_get_item. Use libofcongress_search to discover item IDs first.

Write the item ID with its slashes intact — libofcongress://item/sn95047246/1935-09-05/ed-1 is the canonical form for a multi-segment newspaper ID. Percent-encoded slashes (%2F) also resolve.

Features

Built on @cyanheads/mcp-ts-core:

• Declarative tool and resource definitions — single file per primitive, framework handles registration and validation
• Unified error handling — handlers throw, framework catches, classifies, and formats
• Pluggable auth: none, jwt, oauth
• Swappable storage backends: in-memory, filesystem, Supabase, Cloudflare KV/R2/D1
• Structured logging with optional OpenTelemetry tracing
• STDIO and Streamable HTTP transports

LOC-specific:

• Module-level rate-limit enforcement: 20 req/min limit; 429 responses trigger a 1-hour block with per-minute countdown in error messages
• Configurable pacing delay (default 3100ms, ~19 req/min) applied before every outbound LOC API request
• HTML-response detection guards against silent rate-limit proxy pages that return 200 with HTML
• Out-of-range page handling: LOC returns HTTP 400 or 520 for page numbers beyond the result set — treated as empty rather than errors
• Transient-fault resilience: network drops and timeouts retry with backoff behind a 30s per-request timeout ceiling; the 429 rate-limit path is never retried, since a retry would deepen LOC's 1-hour block
• JSON OCR extraction for newspaper text — reads the full_text field from LOC text-services responses
• Two-service architecture: LocApiService for www.loc.gov and LcLinkedDataService for id.loc.gov

Agent-friendly output:

• Empty results always include a notice field with recovery hints — echoes the applied filters and suggests how to broaden
• Pagination status on every search response: total, page, pages, has_next — capped at LOC's ~100,000-item retrieval ceiling, with a notice disclosing how to page past it
• ocr_available discriminator on newspaper page results so callers can branch on data availability without parsing text
• Recovery hints on all error contracts — actionable next steps for the agent on every failure mode

Getting started

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