> 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/talus-docs-v2.1.0/guides/tool-development.md).

# Tool Development

{% hint style="info" %}
**Audience:** Nexus adopters and integrators.

**Goal:** Choose the Tool development path that produces a registered, callable, and verifiable capability for a workflow.
{% endhint %}

Tool development starts with the runtime contract appropriate to the work:

Before starting either on-chain path, complete [Prepare for On-Chain Development](/talus-docs-v2.1.0/guides/getting-started/prepare-onchain-development.md). It establishes the public Move Registry dependencies, selected-network package IDs, and committed `Move.lock` required before writing, building, upgrading, or publishing Move code. The public [Nexus SDK](https://github.com/Talus-Network/nexus-sdk) and published crates remain the source for off-chain Tool development.

* Use the Rust toolkit to implement `NexusTool`, bootstrap an HTTP server, and [build an off-chain Tool](/talus-docs-v2.1.0/guides/tool-development/build-offchain-tool.md). The generated API reference lives at [Toolkit Rust](/talus-docs-v2.1.0/reference/toolkit.md), and [Tool communication](/talus-docs-v2.1.0/guides/tool-development/tool-communication.md) explains the transport boundary.
* Use Sui Move to [build an on-chain Tool](/talus-docs-v2.1.0/guides/tool-development/build-onchain-tool.md) whose witness, inputs, and durable `OnchainToolResult` are registered with Nexus.
* When an existing on-chain Tool must adopt a compatible package or Nexus dependency upgrade, first [verify the candidate](/talus-docs-v2.1.0/guides/tool-development/build-onchain-tool-vertex-and-upgrade.md#verify-the-candidate), then [upgrade the on-chain Tool](/talus-docs-v2.1.0/guides/tool-development/build-onchain-tool-vertex-and-upgrade.md) while preserving its registered identity.


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