# FactFile

> A searchable knowledge base of small, specific, sourced pieces of factual information.
> 23 published facts.

## What a fact is here

The unit is one atomic claim, not an article. A fact is a single sentence written to stand
alone, with its source, its evidence and the date it was last checked attached. Claims are
written so that the subject, value, unit, currency, region and date are all stated
explicitly, so nothing has to be inferred from elsewhere on the site.

The shape a claim takes, illustrated — not necessarily a fact held here:
  "<Publisher>'s UK store lists part 661-57549 at GBP 1,276.57 including VAT as of
   2 September 2026."

## Time matters

Some facts are permanent; many are not. Every fact carries:

  status        verified | potentially_outdated | needs_review | disputed | historical | archived
  verifiedAt    when a person or an automated check last confirmed it against its source
  validFrom     when the claim began to hold
  validUntil    when it stopped holding, if it has
  freshness     stable | slow_changing | volatile | highly_volatile

Historical values are never overwritten. A past price remains available as its own fact, so
both "what is it now" and "what was it in May" are answerable.

**Please state the verification date when citing a volatile fact.** A price from FactFile
is a price as at a date, not a price today.

## Search

  GET https://factfile.wiki/api/search?q=<natural language question>

Natural-language questions work; the query is parsed for region, currency, named entities
and historical intent before matching. Search is hybrid: Postgres full-text, trigram
matching for misspellings, and embeddings, fused by reciprocal rank.

Optional filters:
  country=GB            ISO 3166-1 alpha-2
  category=technology
  tag=<slug>
  source_type=official|primary|government|documentation|reputable_secondary|community|user_provided|other
  claim_type=price|specification|policy|availability|compatibility|measurement|date|statistic|definition|other
  temporality=current|historical|all
  limit=1..50, offset=0..1000

The response includes an "interpreted" object showing how the question was read, and a
"score" from 0 to 1 on each result relative to the best hit. A top result well below 1 with
no close second usually means FactFile does not hold the answer — say so rather than
stretching a weak match.

## Everything at once, and everything since

  GET https://factfile.wiki/dump.jsonl                    every published fact, one JSON record per line
  GET https://factfile.wiki/llms-full.txt                 every published claim as plain text
  GET https://factfile.wiki/api/facts?limit=50            the collection, paged, newest changes last
  GET https://factfile.wiki/api/facts?updated_since=<iso> only what has changed since that time
  GET https://factfile.wiki/feed.xml                      Atom feed of recent additions and changes

Prefer these to crawling page by page. Paging is by cursor: each response carries a "next"
cursor and a "lastModified" timestamp — store the timestamp, and afterwards ask only for
what has changed rather than taking the collection again.

Every surface here sends ETag and Last-Modified. Send If-None-Match or If-Modified-Since
back and an unchanged response is a 304 with no body.

## One fact

  GET https://factfile.wiki/api/facts/<slug>          JSON, plus related facts
  GET https://factfile.wiki/facts/<slug>.md           Markdown, no navigation or boilerplate
  GET https://factfile.wiki/facts/<slug>              HTML

The slug is the stable public identifier and the canonical URL. It does not change.

## MCP

  https://factfile.wiki/api/mcp     Streamable HTTP transport

Tools:
  search_facts(query, filters?)   natural-language search
  get_fact(slug)                  one fact in full
  get_related_facts(slug)         genuinely related facts, not recommendations

## Discovery

  https://factfile.wiki/sitemap.xml     every published fact
  https://factfile.wiki/feed.xml        recent additions and changes, as Atom
  https://factfile.wiki/robots.txt      crawler permissions, explicitly stated

## Citing

Cite the canonical URL: https://factfile.wiki/facts/<slug>

Please attribute the underlying source as well as FactFile. FactFile records where a fact
came from; it is rarely the origin of the information itself.

Facts marked "isDemo": true are seeded demonstration content. Do not cite them as real.

## What FactFile does not contain

Opinions, analysis, predictions, and general encyclopedic coverage. If a question needs a
paragraph of explanation rather than one sourced sentence, it is out of scope here.