Export specifications.

Documented, versioned, open. Built so a future tool can read your data even if we're gone.

1. JSON — enginehourslog.export v1.0

A single file containing every engine, every hours reading, and every part/service record in your account. Machine-readable, human-readable, diff-friendly. This is the canonical format; CSV and PDF are derived from it.

Top-level shape

{
  "format": "enginehourslog.export",
  "formatVersion": "1.0",
  "exportedAt": "2026-04-21T14:00:00.000Z",
  "specUrl": "https://enginehourslog.com/export-specs",
  "engines": [ Engine, ... ],
  "logs":    [ LogEntry, ... ],
  "parts":   [ PartRecord, ... ]
}

Engine

Field	Type	Description
id	string (UUID)	Stable identifier. Never reused, never changes.
name	string	Human-readable name ("S/V Driftwood").
identifier	string	Optional serial, hull ID, VIN, or similar.
category	string enum	One of: marine_diesel, outboard, rv, tractor, generator, heavy, mower, other. New categories may be added; consumers should treat unknown values as opaque.
hours	integer	Most recent known hours reading. Computed from the latest LogEntry.
createdAt	string (ISO 8601)	When the engine was added to the log.
updatedAt	string (ISO 8601)	Last mutation timestamp.

LogEntry

Field	Type	Description
id	string (UUID)	Stable identifier.
engineId	string (UUID)	FK to Engine.id.
hours	integer	Hours reading at the moment of this entry.
at	string (ISO 8601)	When the reading was recorded.
note	string	Optional free-text note. May contain newlines.

PartRecord

Field	Type	Description
id	string (UUID)	Stable identifier.
engineId	string (UUID)	FK to Engine.id.
component	string	What was replaced/serviced ("Impeller," "Oil & filter").
hours	integer	Hours at the time of service.
at	string (ISO 8601)	When the service occurred.
vendor	string	Supplier or shop.
partNum	string	Manufacturer part number.
cost	number | null	Cost in the account's default currency.
notes	string	Optional free-text notes. May be paragraphs. May contain newlines.

Compatibility rules

• Minor version bumps (v1.1, v1.2, ...) may add optional fields. Consumers must ignore fields they don't understand. Any field present in v1.0 will retain its meaning.
• Major version bumps (v2.0) may restructure. We will publish a migration tool that converts v1 exports to v2 losslessly before shipping v2.
• No version is ever removed. Today's v1.0 file is readable by every future version of EngineHoursLog and by anyone implementing the spec.
• Unknown enum values (e.g., a future category) must be treated as opaque strings by consumers, not as errors.

2. CSV — v1.0

Three files, RFC 4180 compliant, UTF-8, Unix line endings. Designed for Excel, Numbers, Google Sheets, and every command-line tool that eats CSV.

enginehourslog-engines-YYYY-MM-DD.csv

Columns (in order): id, name, identifier, category, hours, createdAt, updatedAt.

enginehourslog-logs-YYYY-MM-DD.csv

Columns: id, engineId, hours, at, note.

enginehourslog-parts-YYYY-MM-DD.csv

Columns: id, engineId, component, hours, at, vendor, partNum, cost, notes.

Quoting and escaping

• All values are escaped per RFC 4180 — fields containing a comma, newline, or double quote are wrapped in double quotes, and interior double quotes are doubled.
• null is represented as an empty field.
• Newlines within a note or notes field are preserved inside quoted fields. Most spreadsheet applications handle this; simple line-based tools may not.

3. Sale Packet — PDF v1.0

A human-readable report intended for a prospective buyer, a mechanic, a surveyor, or an estate handoff. Letter size (8.5" × 11"). Four pages:

1. Cover. Asset name and identifier; category; current hours; year entered into the log; prepared-for slot; prepared-by slot.
2. Summary. Total hours, years of log history, average annual use, number of entries, number of parts/service events, total documented spend. Data-provenance attestation.
3. Parts & service by component. Grouped by component, most recent first; each group with a rollup line (event count, average interval between events, total cost) and a detailed table (hours, date, vendor/part, cost, and a full-width note row for paragraph-length notes).
4. Hours log in full. Chronological table of every hours reading. Export-format attestation referencing this page and the shutdown guarantee.

The PDF is generated entirely client-side using the browser's native "Save as PDF" print path. No server, no library, no dependencies — the HTML that produces it is simple enough that any future browser can render it unchanged.

Locale

When present on the asset, a locale hint causes the Sale Packet to render in that locale — dates, numbers, currency, and UI chrome. This is because the buyer at the marina speaks the marina's language, not the seller's.

4. If we disappear

Per Terms §7.2, if EngineHoursLog ever ceases operations:

• The export tool remains online for at least twelve months after the shutdown announcement.
• This specification page remains public, hosted on an endowment-funded static mirror. (By the time we're close to shutting down, we will publish the archival-mirror URL here.)
• Any user who previously exported their data can continue using it with any tool that implements this specification.

5. Implementing against this spec

If you want to build something that reads or writes EngineHoursLog exports — a backup tool, a migration script, a second implementation of the app — you don't need our permission. Use the formats on this page. Open an issue on our public issue tracker (link coming) if you find ambiguities. We will update the spec to clarify.

If you want to use this spec as the basis for your own logbook and call it EngineHoursLog, please don't — the brand is ours. The data formats, however, are open for anyone to implement.