Designing an On-Chain Price Oracle in Substrate

Nikolai Shelekhov — Sun, 09 Nov 2025 00:00:00 +0000

Accurate price data is foundational to any DeFi system.</p>

DEXs, lending protocols, liquidations, MEV strategies —
all depend on reliable and timely asset pricing.</p>

Instead of relying purely on external infrastructure, I wanted to explore a runtime-native approach using Substrate.</p>

The Goal</h2>
Design a modular price oracle pallet that:</p>

Fetches asset prices from external sources</li>
Aggregates them deterministically</li>
Stores them on-chain</li>
Exposes them to other runtime modules</li> </ul>
The constraint: maintain composability and determinism at the runtime level.</p>
Architecture Overview</h2>
The design uses Substrate’s off-chain workers:</p>

Off-chain worker fetches external price data</li>
Data is validated and formatted</li>
An unsigned transaction submits updated price information</li>
Runtime storage is updated</li> </ol>
This keeps:</p>

Network requests off the runtime path</li>
Deterministic execution within the state machine</li>
Minimal trust assumptions beyond data sources</li> </ul>
Key Design Decisions</h2>
1. Off-Chain Workers</h3>
External HTTP requests cannot block runtime execution.</p>
Off-chain workers allow background fetching without compromising block production.</p>
2. Fixed-Point Arithmetic</h3>
Floating-point operations are not deterministic across architectures.</p>
All price calculations use fixed-point arithmetic to ensure:</p>

Deterministic execution</li>
Predictable rounding</li>
Cross-node consistency</li> </ul>
3. Storage Layout</h3>
Prices are stored in optimized maps keyed by asset identifiers.</p>
Design priorities:</p>

Fast reads (price access is frequent)</li>
Minimal storage overhead</li>
Clear upgrade path</li> </ul>
Why Not Just Use an External Oracle?</h2>
External oracle networks are powerful — but they introduce:</p>

Latency</li>
Trust layers</li>
Dependency on third-party infrastructure</li> </ul>
Embedding oracle logic inside the runtime:</p>

Improves composability</li>
Reduces architectural complexity</li>
Enables tighter integration with DeFi pallets</li> </ul>
For experimentation and MEV research, this approach gives full control over the data lifecycle.</p>
What I Learned</h2>
Building runtime logic reinforces an important principle:</p>
Blockchain development is systems programming.</p>
You’re writing deterministic state machines, with strict performance constraints, and zero room for undefined behavior.</p>
Rust and Substrate make that not only possible — but enjoyable.</p>