libofcongress-mcp-server MCP Server

Search LOC digital collections, Chronicling America newspapers (full OCR), and LC Subject Headings.

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Status

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Connect

Published as @cyanheads/libofcongress-mcp-server on npm. Runs locally.

Known issues

40 problems reported by people outside the maintainer team. Issues filed by the project's own owners, members and collaborators are excluded — those are release checklists and internal refactors, not things that will go wrong for you. Showing 12.

Most discussed

bug(loc_get_item,loc_get_newspaper_page): internal LOC API URL with query params leaked in not-found error messages

Not-found errors from libofcongress_get_item, libofcongress_get_newspaper_page, and the libofcongress://item/{item_id} resource expose the full internal LOC API URL — including query parameters like ?fo=json&at=item,resources,related_items — in data.url. The same leak occurs in serviceUnavailable errors when the LOC API returns an HTML body instead of JSON (rate-limited or maintenance page).

Steps to reproduce

1. Call libofcongress_get_item with input: `{ "item_id": "TOTALLY_

Read the thread · 2026-05-24 · closed · 6 comments

bug(loc_get_item): format() truncates related_items at 5 without indicating truncation — parity gap with structuredContent

Server version

0.1.0

mcp-ts-core version

0.9.9

Runtime

Node.js

Runtime version

Node v25.9.0

Transport

HTTP (Streamable HTTP)

Description

libofcongress_get_item's format() caps both related_items and resource_links at 5 entries in content[]. Originally this was a silent drop (see comments below); a first fix added an "… and N more" overflow note to both blocks. Reopened: disclosure isn't the same as access. An overflow count tells a content[]-onl

Read the thread · 2026-05-24 · closed · 5 comments

bug(search_subjects): returns non-LCSH authority records

Server version

0.2.10

mcp-ts-core version

^0.10.9

Runtime

Bun

Runtime version

Bun 1.3.11

Transport

HTTP

Description

libofcongress_search_subjects is described as returning Library of Congress Subject Headings for use as the subject filter in libofcongress_search, but the live endpoint response includes name-authority and children-subject records ahead of real subject headings. That can send callers to labels that are not LCSH subject headings and may not

Read the thread · 2026-06-27 · closed · 3 comments

feat(get_item): expose research-critical metadata currently discarded

libofcongress_get_item describes itself as returning the full metadata record, but normalization drops several high-value fields already present in the requested item payload. The gap is most consequential for summaries, catalog identifiers, language/location context, and access restrictions.

Proposal

Expand the existing output with a curated set of research-critical fields rather than forwarding raw LOC JSON: summary, languages, locations, call_number, former_ids, `original_f

Read the thread · 2026-07-16 · closed · 2 comments

feat(search): add collection_slug to complete the browse-to-search workflow

libofcongress_browse_collections returns stable collection slugs, but no MCP tool can use them to search inside that collection. The design documentation already describes the slug as a libofcongress_search input, while the actual search schema has no collection/part-of filter.

Proposal

Add an optional collection_slug parameter to libofcongress_search. When present, route the existing query/filter/pagination shape through the corresponding collection endpoint so browse results becom

Read the thread · 2026-07-16 · closed · 2 comments

Most recent

bug(errors): item_not_found and page_not_found reach the client with no recovery hint

Server version

0.2.16

mcp-ts-core version

0.10.14

Runtime

Bun

Runtime version

Bun 1.3.x

Transport

HTTP

Description

The item_not_found and page_not_found contract entries declare useful recovery metadata, but neither throw site passes { recovery: { hint } }, so nothing reaches the wire. Both re-throw the service's message verbatim, and on a 404 that message is the generic notFound('LOC resource not found') raised inside fetchJson — it never names the

Read the thread · 2026-08-10 · open · 0 comments

feat(get_newspaper_page): request at=item,resource so newspaper_title, state, and edition stop coming back empty

Use case

libofcongress_get_newspaper_page declares newspaper_title, state, and edition in its output schema, and never populates any of them. The request asks LOC for ?fo=json&at=resource, and that projection returns exactly seven keys — fulltext_file, iiif_manifest_url, image, pdf, segment_count, url, word_coordinates. The title, date_issued, part_of, and sequence the handler reads are all null there, so state and edition are always absent and `part_of

Read the thread · 2026-08-10 · open · 0 comments

bug(search_subjects): count is the suggest endpoint's record tally, not the LOC item count it is described as

Server version

0.2.16

mcp-ts-core version

0.10.14

Runtime

Bun

Runtime version

Bun 1.3.x

Transport

HTTP

Description

libofcongress_search_subjects describes count as "Approximate number of LOC items carrying this heading." It is parsed from the third array of the id.loc.gov /suggest/ OpenSearch response, which carries a per-suggestion description string — "1 result", "2 results" — counting matching authority records, not catalogued items. parseInt r

Read the thread · 2026-08-10 · open · 0 comments

bug(pagination): LOC 404s out-of-range pages, so recovery guidance is skipped and a valid collection_slug is reported missing

Server version

0.2.16

mcp-ts-core version

0.10.14

Runtime

Bun

Runtime version

Bun 1.3.x

Transport

HTTP

Description

fetchSearchJson treats only HTTP 400 and 520 as "page out of range" (allowStatus: [400, 520] → null → the pages: 0 sentinel handlers key their recovery notice on). LOC actually answers a past-the-end page with 404 on every endpoint except /search/:

Read the thread · 2026-08-10 · open · 0 comments

bug(get_item): object-form item.related_items violates the output schema and fails the call

Server version

0.2.16

mcp-ts-core version

0.10.14

Runtime

Bun

Runtime version

Bun 1.3.x

Transport

HTTP

Description

libofcongress_get_item fails outright for any item whose item.related_items entries are objects rather than strings. RawLocItemResponse types the field as string[] and getItem spreads it straight into the normalized related_items: string[]:

relatedItems.push(...(item.related_items ?? []));

LOC returns objects (`{ title, url

Read the thread · 2026-08-10 · open · 0 comments

bug(tests): LOC_REQUEST_DELAY_MS override is a no-op, so the mocked suite sleeps ~137s

Server version

0.2.12

mcp-ts-core version

0.10.14

Runtime

Bun

Runtime version

Bun 1.3.14

Transport

stdio

Description

bun run test takes ~137s. The same suite with LOC_REQUEST_DELAY_MS=0 in the environment takes ~975ms — a ~140x difference on a suite that mocks fetch and never reaches the network. The suite already tries to disable pacing per test, but the override never takes effect.

The cause is an ordering/caching interaction:

• getServerConfig() me

Read the thread · 2026-07-16 · closed · 1 comment

bug(browse_collections): returned slugs do not match LOC collection routes

Server version

0.2.12

mcp-ts-core version

0.10.14

Runtime

Bun 1.3.14

Transport

HTTP

Description

libofcongress_browse_collections describes slug as the identifier within loc.gov collection URLs, but the extractor only matches URLs ending immediately after /collections/<slug>/. Current LOC results end in /about-this-collection/, so the regex misses and fabricates a title-derived fallback that often is not a valid route.

Steps to reproduce

1. Call `libofco

Read the thread · 2026-07-16 · closed · 1 comment

See all 21 reports Pod holds for libofcongress-mcp-server — of 40 qualified upstream.

Firsthand observations

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For agents

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