Price Sources

Rubicon fetches ETF prices from professional data providers. This page documents our sources and methodology.

Design Philosophy

We fetch ETF prices directly — never constructing synthetic baskets.

Why this matters:

• ETF providers (BlackRock, Samsung, etc.) handle basket composition

• They manage rebalancing, dividends, corporate actions

• Our price matches what you could actually trade

• No drift, no complexity, no failure modes

Primary Source: Yahoo Finance

Overview

Property	Value
Provider	Yahoo Finance
Type	Unofficial API
Coverage	Global equities, ETFs
Latency	200-500ms typical
Update Frequency	~1 minute delay

Data Flow

Yahoo Finance → HTTPS request → Parse → Validate → Oracle

Use Cases

• Primary source for SOXX (US ETF)

• Primary source for Korean ETF prices (.KS tickers)

• Global coverage including international markets

Reliability

• No official SLA

• May have occasional outages

• Rate limiting possible

Limitations

• Not officially supported API

• Slightly delayed quotes

• May change without notice

Backup Source: Polygon.io

Overview

Property	Value
Provider	Polygon.io
Type	REST API
Coverage	US equities, ETFs
Latency	<100ms typical
Update Frequency	Real-time during market hours

Data Flow

Polygon API → HTTPS request → Parse response → Validate → Oracle

Endpoints Used

GET /v2/aggs/ticker/{ticker}/prev
GET /v2/last/trade/{ticker}

Use Cases

• Backup when Yahoo unavailable (SOXX only)

• Lower latency alternative during market hours

Reliability

• Uptime SLA: 99.9%

• Failover: Automatic fallback to cache if both sources fail

Limitations

• Requires API key

• Rate limits apply

• US equities only (not Korean)

Tertiary: Stale Cache

Overview

When both primary and secondary sources fail, we fall back to cached prices.

Property	Value
Max Staleness	60 seconds
Storage	./data/oracle-state.json
Trigger	3 consecutive source failures

When Cache Is Used

1. Both Yahoo and Polygon return errors

2. Network connectivity issues

3. Rate limiting on all sources

Safeguards

• Prices older than 60s trigger alerts

• UI indicates "stale" status

• Continued staleness halts new position opening

Source Priority

┌─────────────────┐
│  1. Yahoo       │ ← Try first (global coverage, primary)
└────────┬────────┘
         │ Failed?
         ▼
┌─────────────────┐
│  2. Polygon     │ ← Try second (US only, backup for SOXX)
└────────┬────────┘
         │ Failed?
         ▼
┌─────────────────┐
│  3. Cache       │ ← Emergency fallback (max 60s stale)
└────────┬────────┘
         │ Too stale?
         ▼
┌─────────────────┐
│  DEGRADED MODE  │ ← Alerts, potential trading halt
└─────────────────┘

Price Validation

Before accepting a price, we validate:

Range Check

Price must be within ±20% of last known price

Protects against erroneous data.

Staleness Check

Timestamp must be within expected update window

Rejects outdated quotes.

Format Check

Price must be positive number with valid precision

Catches parsing errors.

Source by Asset

Asset	Primary	Secondary	Notes
SOXX	Yahoo	Polygon	Full US market hours
091160.KS	Yahoo	—	Korean market hours
396500.KS	Yahoo	—	Korean market hours
395270.KS	Yahoo	—	Korean market hours
091230.KS	Yahoo	—	Korean market hours

FX Rates

For Korean ETFs (priced in KRW), we also fetch:

KRW/USD rate → Convert ETF price to USD → Submit to oracle

FX source: Yahoo Finance KRW=X

Monitoring

We monitor source health:

Metric	Alert Threshold
Error rate	>5% in 5 minutes
Latency	>2 seconds
Consecutive failures	>3

Alerts notify the operations team for immediate response.