QuickStart

Audience: New developers; first contact with Overledger Fusion. Reading time: ~10 minutes. Prerequisites: A terminal with curl and jq installed. An email address (for sign-up). You'll learn: How to get an API key, find your Fusion user ID, browse the available Overledger Fusion Flows, and run your first Flow App session — both in the Quant Connect UI and via the REST API.

This QuickStart takes you from "I have nothing" to "I have run a Flow App session" in around 10 minutes. Every step is shown two ways: in the Quant Connect UI (point-and-click) and via the REST API (curl). Pick whichever you prefer — they drive the same backend.

You will need:

• A terminal with curl and jq installed (for the API route).
• An email address to register a Quant Connect account.

2.1 Get an API key

You mint API keys yourself from your Quant Connect account.

1. Sign up at Quant Connect, verify your email, and sign in.
2. Open the API Keys page and click Create API Key. Optionally give it a label (e.g. my-laptop) so you can recognise it later, then confirm.
3. Copy the key from the API Key Created dialog and store it securely — for security it is shown once and cannot be recovered.

👍

Tip, Prefer the API?

You can also mint a key programmatically using your JWT session token — see chapter 3.2 for the full REST walkthrough.

The API key has the form fk_<keyId>.<secret> and authenticates both RPC and REST requests. The rest of this QuickStart assumes you have it to hand.

2.2 Find your Fusion user ID

Your Fusion user ID is the identity every API key, session, and Flow App action is attributed to. It's the first thing to confirm — checking it also verifies that your API key authenticates correctly.

In Quant Connect: open the API Keys page. Your User ID is shown at the top, with a copy button next to it.

Via the API: pass your API key in the X-API-Key header and call GET /users/me/id:

export OVERLEDGER_URL="https://fusion-rollup.quant.dev"
export API_KEY="<paste your API key>"

curl -s "$OVERLEDGER_URL/users/me/id" \
  -H "X-API-Key: $API_KEY" | jq

Expected response:

{
  "userId": "user_abc"
}

This call returns the identity your key resolves to — so a 200 with your userId also confirms the key works. If you instead get 401, double-check the header is exactly X-API-Key: <your-api-key> (no quotes around the value).

2.3 Browse the Overledger Fusion Flows

Flow Apps are the guided, step-by-step workflows Fusion exposes (signing, contract calls, cross-chain operations, and more). Before running one, see what's available to your account.

In Quant Connect: open the Overledger Fusion Flows page. Each app shows its name, description, and category. The list reflects exactly the apps your account can run.

Via the API: list the registered apps, then inspect one:

# List the apps available to your key
curl -s "$OVERLEDGER_URL/flow/registry/apps" \
  -H "X-API-Key: $API_KEY" | jq '.data[] | {appId, displayName, categories}'

# Inspect a single app. The appId contains a "/", so URL-encode it as "%2F"
# in the path (e.g. quant/dlt-reader -> quant%2Fdlt-reader).
curl -s "$OVERLEDGER_URL/flow/registry/apps/quant%2Fdlt-reader" \
  -H "X-API-Key: $API_KEY" | jq

The registry is the authoritative, per-account source of truth for which apps and versions you can run — see chapter 6.4.

2.4 Run your first Flow App session

A Flow App session is a short-lived state machine: you start it, the server returns a StepSpec (a typed description of the next screen), and you submit input back to advance. For your first run, use the DLT Reader app — a simple, read-only app that fetches on-chain data (account balances, transactions, blocks, and contract reads) across any Fusion-connected network. It needs no funds and signs nothing, so it's the easiest way to see the session loop end to end.

In Quant Connect: open Overledger Fusion Flows, select DLT Reader, and start a session. Pick a read type (e.g. Account Balance), fill in the fields (network and address), and submit — the result renders on the next step.

Via the API: start a session, then read the first step:

# 1. Start a DLT Reader session (the appId goes in the JSON body, no encoding needed)
SESSION=$(curl -s -X POST "$OVERLEDGER_URL/flow/sessions" \
  -H "X-API-Key: $API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"appId":"quant/dlt-reader"}')

export SESSION_ID=$(echo "$SESSION" | jq -r .sessionId)
export STEP_ID=$(echo "$SESSION" | jq -r '.stepSpec.id')

# 2. Re-fetch the same step (idempotent)
curl -s "$OVERLEDGER_URL/flow/sessions/$SESSION_ID/steps/$STEP_ID" \
  -H "X-API-Key: $API_KEY" | jq '.stepSpec'

The response is a StepSpec — typed fields, options, and actions describing the screen. Submit user input back to the same endpoint with POST and a required Idempotency-Key header to advance the session. The complete pattern is in chapter 6.2, and the three ways to consume Flow Apps (UI, MCP for agents, direct HTTPS) are in chapter 6.3.

2.5 Next steps

You now have an API key, your user ID, and a completed Flow App session. From here you can explore the wider platform — each area is available both in Quant Connect and via the API.

Browse the connected networks. See the DLT networks Fusion connects to and their details.

• Quant Connect: My Networks → Network Explorer.
• API: GET /networks (and GET /networks/fusion for the Fusion rollup connected networks).
• Learn more: chapter 5 and the resource model in chapter 4.3.

Connect your own nodes. Register a public node (that others can use) or a private node (that only you can use).

• Quant Connect: My Networks → Node Manager (see chapter 5.2 — Add a node via the Quant Connect UI).
• API: the node and network endpoints, covered in chapter 5.

Explore the Fusion Rollup pages. The Fusion Rollup section of Quant Connect groups the rollup-specific tools:

• Rollup Home — live network status (block height, gas, LIVE/SYNCING/PAUSED).
• Transaction Explorer — your transaction history on the rollup.
• Fusion Firewall — manage which users may interact with your deployed contracts (permissions & visibility).
• Fusion Interchange — move tokens between L1 and the Fusion Rollup.
• API & concepts: chapter 8 for architecture, chain IDs, deposits, and withdrawals; chapter 9 for permissions.