> ## Documentation Index
> Fetch the complete documentation index at: https://agenticadvertisingorg-snap-format-preview-links.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# L0 — Wire & transport

> Wire-and-transport layer of the AdCP stack. JSON-over-HTTP framing, MCP message envelopes, A2A SSE streams, schema validation, language-native type generation.

L0 takes protocol bytes off the wire and turns them into typed in-memory values, or serializes outbound requests against the published schemas. Symmetric on both sides — same primitives, mirrored direction.

## What an SDK at L0 must provide

If you're picking an SDK or porting one to a new language, this is the L0 build target:

* **Generated language-native types** from the published JSON schemas (one type per request/response pair, plus shared resource types).
* **A schema validator** wired against the bundled schemas — so adopters can validate inbound and outbound payloads without hand-rolling the schema-loading dance.
* **Transport adapters** for at least one of \{MCP, A2A}; ideally both. These typically wrap upstream protocol SDKs rather than reimplementing them.
* **A schema-bundle accessor** that finds the right schema files for the active AdCP version without forcing the adopter to hardcode paths.

For the cumulative cross-layer story (what L0+L1+L2+L3 buys you), see the [SDK stack reference](/docs/building/cross-cutting/sdk-stack#l0--wire--transport).

## Pages in this layer

* **[Schemas](/docs/building/by-layer/L0/schemas)** — schema bundle, supply-chain verification, type generation, version pinning.
* **[MCP guide](/docs/building/by-layer/L0/mcp-guide)** — `tools/call` envelope, JSON-RPC 2.0, transport adapter shape.
* **[A2A guide](/docs/building/by-layer/L0/a2a-guide)** — SSE event streams, task framing, artifact extraction.
* **[A2A response format](/docs/building/by-layer/L0/a2a-response-format)** — A2A wire-format reference.
* **[MCP response extraction](/docs/building/by-layer/L0/mcp-response-extraction)** — parsing `tools/call` responses to typed values.
* **[A2A response extraction](/docs/building/by-layer/L0/a2a-response-extraction)** — parsing A2A streams and artifacts.