> For the complete documentation index, see [llms.txt](https://docs.talus.network/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.talus.network/guides/nexus-api/tutorial.md).

# Build a dApp on Nexus API

{% hint style="info" %}
**Audience:** A developer with a terminal, curl, and Node 18+ who wants a first working integration against the hosted Nexus API.

**Goal:** Configure a provider-issued key, read indexed resources, stream events, assemble a raw-HTTP Run Watcher, and port that consumer boundary to React.
{% endhint %}

This tutorial is one continuous hosted-service consumer build. Each step calls the public REST/SSE boundary.

| Step                                                                        | You do                                                  | You end up with                                           |
| --------------------------------------------------------------------------- | ------------------------------------------------------- | --------------------------------------------------------- |
| [1. Configure access](/guides/nexus-api/tutorial/01-get-a-key.md)           | Receive a provider-issued key and store it safely       | A scoped key held only by your server-side shell or relay |
| [2. Read the network](/guides/nexus-api/tutorial/02-read-the-network.md)    | List resources, follow pagination, and inspect an error | REST calls the dApp can render                            |
| [3. Stream events](/guides/nexus-api/tutorial/03-stream-events.md)          | Open SSE, filter kinds, disconnect, and resume          | A replayable live signal with a cursor                    |
| [4. Assemble the dApp](/guides/nexus-api/tutorial/04-assemble-the-dapp.md)  | Paste one raw-HTTP relay and Run Watcher                | A same-origin browser view with no browser key            |
| [5. Port the dApp to React](/guides/nexus-api/tutorial/05-port-to-react.md) | Use page-local public types with fetch and EventSource  | The same dApp in a typed React app                        |

The architecture figure keeps the API key on the server side while the browser receives only the app's public response and event state. REST renders the live projection; SSE wakes the app to re-read and recover.

```mermaid
sequenceDiagram
  participant Builder
  participant Provider
  participant Relay
  participant API as Hosted Nexus API
  participant Browser
  Provider-->>Builder: Deliver scoped API key through secure channel
  Builder->>Relay: Configure provisional URL and secret
  Browser->>Relay: Request same-origin resource
  Relay->>API: Add x-api-key and forward request
  API-->>Relay: JSON or SSE with status and diagnostics
  Relay-->>Browser: Public response without secret
  Browser->>Relay: Reconnect with last event cursor
  Relay->>API: Request retained replay when supported
```

The sequence is the complete external trust boundary: the provider provisions access, your relay protects it, and the browser never receives or logs the credential. Cursor retention, reset behavior, keep-alive cadence, and duplicate delivery remain provider-specific; validate frames and follow the provider's `/openapi.json` or published stream policy. Start with [Step 1](/guides/nexus-api/tutorial/01-get-a-key.md), then keep the same cleanup boundary as you move through the shell examples.

Set a clearly provisional endpoint before starting:

```bash
# mainnet
export NEXUS_API_URL="https://api.taluslabs.dev"

# testnet
export NEXUS_API_TESTNET_URL="https://api-testnet.taluslabs.dev"
```

When a response surprises you, use [Nexus API Troubleshooting](/guides/nexus-api/troubleshooting.md). For exact paths, scopes, status values, and envelopes, use the [HTTP API reference](https://api.taluslabs.dev/docs).


---

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