Overview
Route hints are optional pieces of routing information embedded in a Lightning invoice that help the sender find a payment path to the recipient. They are essential when the recipient's node is connected to the network through private (unannounced) channels that do not appear in the public network graph. Without route hints, the sender's routing algorithm would have no way to discover the last-mile path to the recipient, and the payment would fail.
On the Lightning Network, nodes gossip channel information to build a shared view of the network topology. However, not all channels are announced publicly. Mobile wallets, privacy-focused nodes, and nodes behind Lightning Service Providers often use private channels that are not broadcast to the network. Route hints bridge this information gap by telling the sender exactly how to reach the recipient through these hidden channels.
How Route Hints Work
A route hint contains the minimum information a sender needs to extend their computed route through one or more private channels to reach the recipient. Each hint includes the channel's public key, short channel ID, fee parameters, and timelock requirements.
Public network graph known to sender:
Sender ──► A ──► B ──► C ──► D ──► ???
│
Public │ Private channel
network │ (not in graph)
│
▼
Recipient
Without route hints:
Sender's pathfinding: "I can reach D but I don't
know how to get from D to Recipient. Payment fails."
With route hints in invoice:
Invoice includes: {
node: D,
channel_id: 789xxx,
fee_base: 1000,
fee_rate: 100,
cltv_expiry_delta: 40
}
Sender's pathfinding: "Route to D using public graph,
then use this private channel to reach Recipient."
Sender ──► A ──► B ──► C ──► D ──[hint]──► Recipient
Structure of a Route Hint
Each route hint entry describes one hop and contains:
┌──────────────────────────────────────────────┐
│ Route Hint Entry │
├──────────────────────────────────────────────┤
│ pubkey: Node public key │
│ short_channel_id: Channel identifier │
│ fee_base_msat: Base fee (millisatoshis) │
│ fee_proportional: Proportional fee (ppm) │
│ cltv_expiry_delta: Timelock delta (blocks) │
└──────────────────────────────────────────────┘
An invoice can include multiple route hints,
each describing an alternative path to the recipient.
Multiple hints = multiple private channels = better
payment success rates.
A single route hint can describe a chain of multiple hops if the recipient is several private channels deep. In practice, most route hints describe a single hop from a well-connected public node to the private recipient.
When Route Hints Are Used
Mobile wallets: Most mobile Lightning wallets connect to the network through one or a few channels to an LSP or well-known node. These channels are typically private, so every invoice the mobile wallet generates includes route hints pointing through its LSP.
Privacy-focused nodes: Node operators who prefer not to announce their channels publicly rely on route hints to remain reachable for payments. By keeping channels private, they avoid revealing their channel partners and capacity to the network.
New nodes: A node that has just opened its first channel may not yet have had its channel announcement propagated through the gossip network. Route hints ensure it can receive payments immediately.
Privacy Implications
Route hints reveal information about the recipient's private channel topology. Each hint exposes a channel partner's public key, the channel ID, and fee structure. For this reason, privacy-conscious users should be aware that route hints in invoices can be used to fingerprint their node's connectivity.
Blinded paths (used in BOLT12) offer a more privacy-preserving alternative. Instead of revealing the exact channel and node information, blinded paths encrypt the routing information so the sender can forward the payment without learning the recipient's channel partners or network position.
Impact on Payment Success
Route hints significantly affect payment reliability. An invoice with no route hints for a node reachable only through private channels will always fail. Conversely, including multiple route hints (one for each private channel) gives the sender more options and increases the likelihood of finding a path with sufficient liquidity. Wallet implementations typically include route hints for all available private channels, up to the invoice size limit.
Related Concepts
- Routing — the path-finding process that consumes route hint information
- Lightning Channel — the private channels that route hints describe
- Lightning Invoice — the payment request format that carries route hints
- Blinded Paths — a privacy-enhanced alternative to route hints
- Lightning Service Provider — commonly the node at the other end of a route hint for mobile wallets