> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.nvidia.com/nemo/relay/dev/about-nemo-relay/concepts/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.nvidia.com/nemo/relay/_mcp/server.

# Concepts

Use these pages to understand the NeMo Relay runtime model before applying it
in a use-case workflow.

NeMo Relay's shared runtime model has five parts:

* **Scopes** decide where work belongs and which scope-local behavior is visible.
* **Events** record what happened in the canonical lifecycle stream.
* **Middleware** decides what can block, rewrite, sanitize, or wrap managed
  execution.
* **Plugins** install reusable runtime behavior from configuration.
* **Subscribers and exporters** consume that stream in process, write raw ATOF
  events, or project events into downstream formats.

Managed tool and LLM helpers are the application-owned API path through scopes,
middleware, events, and subscribers. Codecs are boundary translators that
normalize typed application values or provider-native payloads when runtime
behavior needs stable data shapes.

Use the concepts pages for runtime semantics such as ownership, ordering,
cleanup, and support boundaries. Use the generated [API Reference](/reference/api) for symbol lookup after you already know which
runtime concept or integration boundary you need.

#### [Scopes](/about-nemo-relay/concepts/scopes)

Scope hierarchy, lifetime, and isolation for agent runs, requests, tools, LLM calls, and nested work.

#### [Events](/about-nemo-relay/concepts/events)

Canonical lifecycle records for scopes, tool calls, LLM calls, marks, subscribers, and exporters.

#### [Middleware](/about-nemo-relay/concepts/middleware)

Guardrails and intercepts that sanitize, transform, block, or wrap tool and LLM execution.

#### [Plugins](/about-nemo-relay/concepts/plugins)

Configuration-driven bundles that install reusable middleware, subscribers, and adaptive behavior.

#### [Subscribers](/about-nemo-relay/concepts/subscribers)

Consumers for lifecycle events, including logs, traces, trajectories, analytics, and diagnostics.

#### [Provider Codecs](/about-nemo-relay/concepts/codecs)

Provider request and response normalization for middleware and observability.

## Docs

- [Scopes](https://docs.nvidia.com/nemo/relay/dev/about-nemo-relay/concepts/scopes.md): Understand scope hierarchy, lifetime, cleanup, and concurrent isolation.
- [Middleware](https://docs.nvidia.com/nemo/relay/dev/about-nemo-relay/concepts/middleware.md): Choose and configure middleware for managed tool and LLM calls.
- [Conditional Middleware Guardrails](https://docs.nvidia.com/nemo/relay/dev/about-nemo-relay/concepts/conditional-middleware-guardrails.md): Understand how Relay controls the eligibility of global runtime registrations.
- [Events](https://docs.nvidia.com/nemo/relay/dev/about-nemo-relay/concepts/events.md): Understand ATOF lifecycle events, fields, relationships, and delivery.
- [Plugins](https://docs.nvidia.com/nemo/relay/dev/about-nemo-relay/concepts/plugins.md): Understand NeMo Relay plugin configuration, lifecycle, ownership, and built-in components.
- [Subscribers](https://docs.nvidia.com/nemo/relay/dev/about-nemo-relay/concepts/subscribers.md): Understand NeMo Relay subscribers, delivery behavior, scope visibility, and exporter roles.
- [Provider Codecs](https://docs.nvidia.com/nemo/relay/dev/about-nemo-relay/concepts/codecs.md): Understand how provider codecs normalize requests and responses, preserve unknown fields, and expose supported fields.