Verified Facts

By Data Butler

Overview

Verified Facts returns one official figure per lookup: you send a key such as uk/income-tax/personal-allowance and an optional max_age, and get back the value, unit and period, the official source URL (gov.uk, IRS, Bundesfinanzministerium, central banks), the date a person last checked it against that source, a fresh or stale flag, and an Ed25519 signature that can be checked against databutler.dev/.well-known/jwks.json. It covers 496 figures: UK income tax, National Insurance, benefits, vehicle tax and MOT rules and government service fees; US federal tax brackets, Social Security, Medicare and retirement limits; German income tax and social-insurance thresholds; Bank of England, Fed and ECB policy rates; UK exam dates. Three read-only tools: get_fact (one or several keys), resolve_fact (turns a plain-language question such as "NI primary threshold" into a key), and what_changed_since (every figure that changed after a given date, with before and after values and sources). No account or API key. The same facts are served as plain web pages at databutler.dev/f/<key> and are described by an open specification, Verified Facts v0.2, at databutler.dev/facts.

Tools

get_fact

Claude

The current value of one official figure by key — a tax threshold, rate, allowance, fee, deadline, limit or policy rate — with the date it was verified, the official source URL, the period it applies to and a signature. Keys are <country>/<topic>/<fact>, e.g. uk/income-tax/personal-allowance, uk/national-insurance/primary-threshold, us/social-security/wage-base, de/income-tax/grundfreibetrag, uk/bank-rate, eu/ecb/deposit-facility, uk/gov/passport-renewal-adult/fee-online-uk. A loose key is resolved when unambiguous; otherwise the answer lists candidate keys. max_age (e.g. 30d) marks the answer stale when the verification is older than that. Several keys separated by commas return a batch. Covers UK, US and German rates and thresholds, UK vehicle tax and MOT rules, UK government service fees, UK exam dates and central-bank policy rates; coverage lists the rest.

resolve_fact

Claude

Ranked canonical fact keys for a plain-language question or a guessed key — "NI primary threshold", "ECB deposit rate", "passport renewal fee" — each with label, unit, period and verification date, and the full record of the top match when it is unambiguous. The keys feed get_fact. Filter by namespace (uk, us, de, eu).

what_changed_since

Claude

What has changed in Data Butler's verified datasets since a date — pass your training-cutoff date to learn which UK tax/NI/benefit thresholds, exam-spec facts, official vehicle datasets (UK DVSA, French RappelConso and Japanese MLIT recalls), software end-of-life dates (Node.js, Python, Ubuntu, Debian, Android, iOS, macOS, Windows, Java, Go, Ruby, PHP, PostgreSQL, React — cycles that reached end of life or whose dates moved), central-bank policy rates (Bank of England, Fed, ECB), US federal tax thresholds (IRS inflation adjustments, Social Security wage base, retirement and HSA limits), German tax and social-insurance thresholds (Grundfreibetrag, Beitragsbemessungsgrenzen, Zusatzbeitrag, Mindestlohn, Kindergeld), UK vehicle tax (VED) rates and MOT rules, UK exam dates (results days, summer timetable paper dates, entry deadlines and late-fee dates, announced specification changes), calendar facts (public holidays for the UK, US, Germany and France; tax-year and daylight-saving rules for nine countries — new years published, holidays added or moved) and UK government service fees and rules (passports, ETA, Universal Credit, eVisa) changed after your knowledge ends. Each entry: from → to, effectiveFrom, official source, verifiedDate, and a maintainer note (e.g. which Budget). Areas: uk-rates, uk-exams, vehicles, software-eol, policy-rates, us-rates, de-rates, uk-vehicle-rules, uk-exam-dates, calendar, uk-gov-process, or all. Coverage starts 2026-08-31. The same changelog is published for humans at https://databutler.dev/changes, with feeds at https://databutler.dev/changes.rss and https://databutler.dev/changes.atom. Output is a Verified Changes protocol document (verified-changes/0.1, spec https://databutler.dev/protocol); an entry whose figure is a Verified Fact carries factKey for get_fact.

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