lnget

lnget is a command-line HTTP client that handles L402 Lightning payments transparently. It was designed for programmatic access to paid APIs—when a server returns HTTP 402 Payment Required, lnget automatically pays the invoice via Lightning and retries the request. No manual intervention, no payment flow interruption.

The Problem

The web is increasingly experimenting with micropayments. L402 (formerly LSAT) enables APIs to charge per-request using Lightning Network invoices. A server responds with 402 Payment Required, includes a macaroon and invoice in the WWW-Authenticate header, and expects the client to pay before retrying.

Existing HTTP clients don't understand this flow. You'd need to parse the challenge header, extract the invoice, switch to a Lightning wallet, pay, extract the preimage, construct the authorization header, and retry. For a single request that's tedious. For automated pipelines or AI agents consuming paid APIs, it's a blocker.

The Solution

lnget handles the entire L402 flow automatically:

lnget https://api.example.com/premium-data.json

If the server returns 402, lnget parses the challenge, pays the invoice through your configured Lightning backend, and retries with the proper Authorization: L402 header. The response streams to stdout or a file, just like wget or curl.

Tokens are cached per-domain, so subsequent requests reuse the paid credential without additional payments:

# First request: pays invoice, caches token
lnget https://api.example.com/data/1

# Second request: reuses token, no payment
lnget https://api.example.com/data/2

Installation

go install github.com/lightninglabs/lnget/cmd/lnget@latest

Or build from source:

git clone https://github.com/lightninglabs/lnget.git
cd lnget
make install

Configuration

lnget needs a Lightning backend to pay invoices. Configure it once:

# Initialize config file
lnget config init

# Edit ~/.lnget/config.yaml with your lnd details

Example config for external lnd:

ln:
  mode: lnd
  lnd:
    host: localhost:10009
    tls_cert: ~/.lnd/tls.cert
    macaroon: ~/.lnd/data/chain/bitcoin/mainnet/admin.macaroon

Or use environment variables:

export LNGET_LN_LND_HOST=localhost:10009
export LNGET_LN_LND_MACAROON=~/.lnd/data/chain/bitcoin/mainnet/admin.macaroon
export LNGET_LN_LND_TLS_CERT=~/.lnd/tls.cert

Verify the connection:

lnget ln status

Usage

Basic usage mirrors wget and curl:

# Download to stdout
lnget https://api.example.com/data.json

# Save to file
lnget -o data.json https://api.example.com/data.json

# Quiet mode for piping
lnget -q https://api.example.com/data.json | jq .

# POST request with data
lnget -X POST -d '{"query": "test"}' https://api.example.com/search

# Custom headers
lnget -H "Accept: application/json" https://api.example.com/data

Payment Controls

Set limits on automatic payments:

# Maximum invoice amount to pay automatically (default: 1000 sats)
lnget --max-cost 5000 https://api.example.com/expensive-endpoint

# Maximum routing fee (default: 10 sats)
lnget --max-fee 50 https://api.example.com/data

# Disable automatic payment (just show the 402 response)
lnget --no-pay https://api.example.com/data

Resume Support

Resume interrupted downloads:

lnget -c https://api.example.com/large-file.zip

If the server supports Range requests and you have a partial file, lnget continues from where it left off.

Token Management

View and manage cached L402 tokens:

# List all cached tokens
lnget tokens list

# Show token for specific domain
lnget tokens show api.example.com

# Remove token (forces re-payment on next request)
lnget tokens remove api.example.com

# Clear all tokens
lnget tokens clear

Output Formats

lnget supports two output modes: human-readable (default for terminals) and JSON (default when piped):

# Force JSON output
lnget --json https://api.example.com/data

# Force human output
lnget --human https://api.example.com/data

JSON output is structured for programmatic consumption:

{
  "url": "https://api.example.com/data.json",
  "status": 200,
  "size": 1024,
  "duration": "0.5s",
  "payment": {
    "amount_sat": 100,
    "fee_sat": 2,
    "preimage": "abc123..."
  }
}

Why This Matters for Agents

AI agents need to consume APIs programmatically. When those APIs require payment, the agent needs a seamless way to authorize and pay without human intervention.

lnget provides:

• Automatic payment flow: No manual steps between 402 response and authorized retry
• Token caching: Pay once, reuse the credential for subsequent requests
• Cost controls: --max-cost prevents runaway spending
• JSON output: Structured responses that agents can parse directly
• Quiet mode: -q suppresses everything except the response body

An agent can call lnget -q --max-cost 1000 https://api.example.com/data | jq .result and get the data, with payment handled transparently in the background.

Lightning Backends

lnget supports multiple Lightning backends:

External lnd

Connect to a running lnd instance:

ln:
  mode: lnd
  lnd:
    host: localhost:10009
    tls_cert: ~/.lnd/tls.cert
    macaroon: ~/.lnd/data/chain/bitcoin/mainnet/admin.macaroon

Lightning Node Connect (LNC)

Connect via LNC pairing phrase for remote nodes:

lnget ln lnc pair "your-pairing-phrase-here"

Then set the backend:

ln:
  mode: lnc

Embedded Neutrino (Experimental)

Run a lightweight SPV wallet directly in lnget:

lnget ln neutrino init

ln:
  mode: neutrino

How It Works

When you run lnget https://api.example.com/data:

1. lnget checks for a cached token for api.example.com
2. If found and valid, includes Authorization: L402 <macaroon>:<preimage> header
3. Makes the HTTP request
4. If server returns 402 with WWW-Authenticate: L402 macaroon="...", invoice="...":
   • Parses the macaroon and invoice from the header
   • Verifies the invoice amount is within --max-cost
   • Pays the invoice via the configured Lightning backend
   • Stores the token (macaroon + preimage) for the domain
   • Retries the request with the authorization header
5. Streams the response to stdout or the output file

Tokens are stored at ~/.lnget/tokens/<domain>/ and persist across invocations.

Exit Codes

Code	Meaning
0	Success
1	General error
2	Payment required but exceeded max cost
3	Payment failed
4	Network/connection error

Development

make build       # build binary
make install     # install to $GOPATH/bin
make unit        # run tests
make lint        # run linters
make fmt         # format code

The codebase follows a functional core / imperative shell pattern:

• l402/ - Token handling, challenge parsing, storage (pure/testable)
• client/ - HTTP client with L402 transport layer
• ln/ - Lightning backend implementations
• cli/ - Cobra command definitions
• cmd/lnget/ - Entry point

See docs/agents.md for architecture details aimed at AI agents working on this codebase.

License

MIT