acta

A multi-currency, double-entry, point-in-time-queryable ledger sandbox for backend engineers.

Latin for "things done." A ledger is a record of things done. Live at acta.rithvikronaldo.dev.

The ledger sandbox you wish existed when you were learning fintech backend. Sign up, get an API key, post your first transaction with curl, and watch it land in a real-time dashboard.

Building notes at rithvikronaldo.dev.

What you can do

• Post balanced double-entry transactions over HTTP, with idempotency keys
• Authorize → capture → void with available / on_hold semantics distinct from realised balance
• Query any account's balance at any past timestamp (?as_of=2026-04-21T14:32:00Z) via a snapshot+delta replay table
• Post transactions in any currency; FX rates are point-in-time too — LookupRate returns the latest observation ≤ your as_of
• Subscribe to /events/stream (Server-Sent Events) and watch transactions land in real time
• Open the live dashboard URL and view a public demo tenant with five named accounts emitting steady traffic — no signup required

Status

Week	Theme	Status
1 (Apr 19–26)	Schema, balanced-entries trigger, POST /transactions	✅
2	Multi-currency FX, point-in-time balance queries, snapshot+delta	✅
3 (May 4-10)	Authorize/capture lifecycle, SSE event stream, transaction list, agents schema	✅
4 (May 4-10)	Frontend dashboard, SSE event stream, ledger-sandbox repositioning	✅
5 (May 11-17)	Multi-tenancy: tenants table, signup endpoint, API key auth, cross-tenant isolation tests, dashboard tenant-switch	✅
6 (May 18-24)	/docs, deploy to acta.rithvikronaldo.dev, launch	🚧

Run it locally

Requires: Go 1.23+, Docker (Colima or Docker Desktop), golang-migrate CLI, make.

# 1. Start Postgres in Docker (port 5433)
make db-up

# 2. Apply schema migrations
make migrate-up

# 3. Load demo fixtures (demo tenant, 4 currencies, 5 named accounts, treasury + vendor pools)
make seed

# 4. Run the API
make run

Then in another terminal:

curl localhost:8080/health
# → {"db":"ok","version":"0.1.0"}

Post a balanced transaction

A guest pays ₹10,000 for a booking. The platform owes ₹8,500 to the host, keeps ₹1,300 as commission, and owes ₹200 in GST.

curl -X POST localhost:8080/transactions \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: booking_B001" \
  -d '{
    "description": "Booking #B001 confirmed",
    "occurred_at": "2026-04-21T14:32:00Z",
    "entries": [
      {"account": "guest_payments", "amount": 1000000, "currency": "INR", "direction": "in"},
      {"account": "host_payable",   "amount": 850000,  "currency": "INR", "direction": "out"},
      {"account": "commission",     "amount": 130000,  "currency": "INR", "direction": "out"},
      {"account": "gst_payable",    "amount": 20000,   "currency": "INR", "direction": "out"}
    ]
  }'

Amounts are in minor units (paise for INR, cents for USD/EUR/GBP), so 1000000 = ₹10,000.00.

Response semantics

Scenario	Status	Body
Balanced	201 Created	Posted transaction with IDs
Retry with same Idempotency-Key	200 OK + Idempotent-Replay: true	Original response bytes, no duplicate write
Σ in ≠ Σ out per currency	422	{"error":"unbalanced","currency":"INR","in":…,"out":…,"diff":…}
Unknown account code	422	{"error":"unknown_account","message":…}
Same key, different body	422	{"error":"idempotency_hash_mismatch",…}
Retry while first is still processing	409	{"error":"idempotency_pending",…}
Malformed JSON	400	{"error":"invalid_json",…}

Authorize / capture / void

# Reserve $5.00 from researcher → vendor pool
curl -X POST localhost:8080/authorizations -d '{
  "source": "agent_<id>_usd", "dest": "vendor_pool_usd",
  "amount": 500, "currency": "USD",
  "description": "cp:openai · researcher call"
}'
# → 201 with auth.id

# Capture $4.30 (balance moves; remainder released)
curl -X POST localhost:8080/authorizations/<auth.id>/capture -d '{"amount": 430}'

# Or release the whole hold without capturing
curl -X POST localhost:8080/authorizations/<auth.id>/void -d '{}'

GET /accounts/<code>/balance returns three numbers: balance (realised), available (balance - sum(pending auths)), and on_hold (sum(pending auths)).

Point-in-time queries

# What was researcher's USD balance at 2:32pm IST on April 21?
curl 'localhost:8080/accounts/agent_<id>_usd/balance?as_of=2026-04-21T14:32:00+05:30'

# Same balance, expressed in EUR using the FX rate current at that timestamp
curl 'localhost:8080/accounts/agent_<id>_usd/balance?as_of=2026-04-21T14:32:00+05:30&in=EUR'

Implementation: a daily account_snapshots table, then SUM over entries after the snapshot's as_of. The LookupRate helper uses WHERE as_of <= $1 ORDER BY as_of DESC LIMIT 1 semantics so historical balances always pick a defensible rate.

Live dashboard

When the API is running, the frontend in web/ is a Next.js 16 / React 19 / Tailwind 4 dashboard:

cd web
npm install --legacy-peer-deps
npm run dev
# → http://localhost:3000

The dashboard subscribes to /events/stream (SSE), maintains state in a Zustand store, animates with Motion v11 (springs, layout transitions, useMotionValue interpolation), and renders all numerics in JetBrains Mono with tabular-nums + slashed-zero. The default view is the public demo tenant — five named accounts (researcher, analyst, writer, coder, translator) emitting authorize/capture/void events at 1.2-3.6s intervals.

There's also a single-file vanilla-JS replica at prototypes/dashboard.html — no build, opens in any browser, useful for blog screenshots and Loom recordings.

Audience

Built for backend engineers exploring or building on double-entry ledgers, multi-currency systems, or point-in-time accounting — particularly at and near Modern Treasury, Increase, Mercury, Bridge, Anrok, Rainforest, Rivet, and crypto exchanges with internal accounting needs.

If you're one of those engineers and want to chat: rithvikronaldo@gmail.com or DM me on the GitHub profile linked in the org.

Development

make test                # run the Go tests
make test-integration    # tests against the live Postgres trigger
make vet                 # static checks
make psql                # shell into the Postgres container
make db-down             # stop Postgres (data persists)
make snapshot            # compute end-of-day account snapshots (default: yesterday UTC)
make snapshot DATE=2026-04-30

License

MIT. See LICENSE.