---
title: "Introduction"
description: "Introduction — the framework-agnostic PHP core (babelqueue/php-sdk): the canonical envelope codec, contracts and dead-letter helpers."
source: https://babelqueue.com/docs/php-sdk/1.x/introduction/
updated: 2026-06-15T00:00:00.000Z
---

# Introduction

`babelqueue/php-sdk` is the framework-agnostic **PHP core**: the wire-envelope
codec, contracts, validation and dead-letter helpers. It is the **single PHP
implementation of the wire format**, so the framework adapters reuse it and can
never drift.

Most PHP applications don't install this directly — they install an adapter, which
pulls the core in:

- **[Laravel](/docs/laravel/1.x/introduction/)** — a drop-in polyglot queue driver.
- **[Symfony](/docs/symfony/1.x/introduction/)** — a Messenger serializer.

Install the core directly only for a **framework-less PHP app**, or to build a new
adapter.

## What you get

- **`EnvelopeCodec`** — build (`make` / `fromJob`), `encode`, `decode`, `urn` and
  `accepts` for the canonical `{job, trace_id, data, meta, attempts}` envelope
  (`schema_version: 1`).
- **Contracts** — `PolyglotJob` (`getBabelUrn()` + `toPayload()`), `HasTraceId`,
  `InboundMessage`, `ConsumedMessage`, and a minimal `Transport` seam.
- **Validation** — `EnvelopeValidator` (consumer-side checks *with a reason*, so you can
  quarantine an unsupported `schema_version` instead of dropping it) and the offline
  `SchemaValidator` (validate any envelope against the bundled canonical JSON Schema).
- **Reference transports** — optional framework-less producers for **all seven brokers**:
  `RedisTransport`, `AmqpTransport`, `SqsTransport`, plus `KafkaTransport` (§6),
  `PulsarTransport` (§5) and `StompTransport` (§7, Artemis).
- **Framework-less consumers** — `KafkaConsumer` (§6 over `ext-rdkafka`, process-then-commit)
  and `PulsarConsumer` (§5 over Pulsar's WebSocket API), plus the §6.4/§6.5 Kafka retry-topic
  machinery (`KafkaRetryRouter` + `KafkaRetryConsumer`).
- **A consume runtime** — `Consume\Dispatcher` (URN → handler routing + the four
  `on_unknown_urn` strategies) and `Consume\DeadLetterPublisher` (route poison messages to
  `<queue>.dlq`).
- **Dead-letter** + **unknown-URN strategies**, and a dependency-free UUIDv4.

**Zero heavy dependencies** — PHP `^8.2` and `ext-json` only; each transport's broker client
is an opt-in suggestion you install only when you use it.

## Core, not a full framework worker

This core is the **contract runtime** plus optional building blocks — the codec, the
transports and the framework-less consume primitives above. It deliberately has no
long-running supervisor, backoff scheduler or process manager: on **Laravel** and **Symfony**
you bind to the framework's native queue (the drop-in driver, Messenger) and reuse that
framework's worker and retry; for a **framework-less** service, the `KafkaConsumer` /
`PulsarConsumer` `consume()` loops + the `Dispatcher` give you a complete consume path on
those brokers.

## The envelope

```json
{
  "job": "urn:babel:orders:created",
  "trace_id": "7b3f9c2a-e41d-4f88-9b2a-1c0d5e6f7a8b",
  "data": { "order_id": 1042 },
  "meta": { "id": "f1e2d3c4-b5a6-4789-90ab-cdef01234567", "queue": "orders", "lang": "php", "schema_version": 1, "created_at": 1749132727000 },
  "attempts": 0
}
```

See the full [wire contract](/docs/spec/1.x/envelope/). Continue to
[Installation](/docs/php-sdk/1.x/installation/).