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You model accounts, post balanced transactions, and read balances over a plain HTTP API. The ledger guarantees the accounting invariants; you write the business logic. You get primitives, not opinions, which is why a treasury startup, a marketplace, an FX desk and a SaaS company billing its own usage all build on the same four.

Post your first transaction

From credentials to a posted transaction, in four calls.

Ledger concepts

Double-entry, corrections, idempotency, multi-currency, value dates.

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The four primitives

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Account

A named bucket of value in one currency. You choose the id, which may hold letters, digits, _, :, . and -, and the currency. Both are immutable once set. Accounts carry one of five accounting types (asset, liability, revenue, expense, equity), which are informational for reporting.

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Posting

One line of a transaction. It says: this account moved by this amount, in this direction (debit or credit), in this currency, effective at this value_date.

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Transaction

A set of postings that move together. The ledger enforces sum(debits) == sum(credits) per currency, and rejects anything that does not balance. That is the whole correctness model. There is no validation of whether a transaction “makes sense”, because the balance rule is what makes a double-entry ledger trustworthy.

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Balance

The net of an account’s postings, now or at a historical instant. Derived from postings, never stored, and computed from value_date rather than insertion time.

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A balanced transaction

Monetary values cross the wire as JSON strings of integer minor units. Parse them with a big-integer type, never a JS number.

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What makes it safe

Append-only

Postings are never edited. You correct with a reversal or a refund that references the original.

Idempotent

Every write carries an Idempotency-Key. A replay returns the original transaction.

Multi-currency

Currency is first class. No code path assumes one, and the balance rule applies per currency.

Reconciliation as a primitive

Replayable runs that match an external snapshot against postings.

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Who uses this

Anyone who needs an auditable record of what money meant, separate from whatever moved it. Kordio’s own spend control is one such customer: where the projection is enabled, agent spend arrives here as balanced postings. The ledger itself knows nothing about agents. It speaks accounts, postings, transactions and balances, and it does not move money either.

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Next steps

Why a ledger API

Versus Postgres, a processor, accounting software, and the other ledger APIs.

API reference

Every endpoint, generated from the OpenAPI spec.