# Extensions

## Intent

Extensions add conditional standards to the baseline stacks. An extension stays inactive until a current requirement meets its activation criteria. The consumer lists its ID in `selectedExtensions` within `litespec.project.json`, with the criterion it met and a review date.

An extension may add requirements, packages, projects, and verification. It replaces a baseline rule only when its document names that provision ID. The manifest repeats that list where checks read it.

## Selection

| Extension | Activation scope | Replaces | Switches on | Activate when |
|:---|:---|:---|:---|:---|
| [bdd](https://litespec.dev/2.0.0/backend/dotnet/ext/bdd.md) | `local` | None | `case` | Shared critical examples need executable BDD scenarios. |
| [compat](https://litespec.dev/2.0.0/ext/compat.md) | `project` | None | None | Public or independently deployed consumers need breaking-change detection and versioning. |
| [cache](https://litespec.dev/2.0.0/ext/cache.md) | `local` | None | `limit` | Measurements show repeated expensive reads with bounded staleness. |
| [concurrency](https://litespec.dev/2.0.0/ext/concurrency.md) | `local` | None | `limit` | Conflicting writes or repeated delivery can violate behavior. |
| [lifecycle](https://litespec.dev/2.0.0/ext/lifecycle.md) | `local` | None | `limit` | Deletion, retention, archival, restore, or legal hold behavior applies. |
| [containers](https://litespec.dev/2.0.0/ext/containers.md) | `project` | None | `limit`, `runbook` | A hosted environment deploys container images. |
| [integrations](https://litespec.dev/2.0.0/ext/integrations.md) | `local` | None | None | Behavior calls or receives data from an external system. |
| [audit](https://litespec.dev/2.0.0/ext/audit.md) | `project` | `litespec/quality/security#record-security-audit-events` | None | A reviewer must establish who acted inside data another party owns. |
| [locale](https://litespec.dev/2.0.0/ext/locale.md) | `project` | None | None | The product commits to more than one locale. |
| [mcp](https://litespec.dev/2.0.0/ext/mcp.md) | `project` | None | None | The product ships a Model Context Protocol server an LLM client starts on a user's own machine. |
| [tenancy](https://litespec.dev/2.0.0/ext/tenancy.md) | `project` | None | None | Independent customer organizations share one deployment. |
| [outbox](https://litespec.dev/2.0.0/ext/outbox.md) | `local` | `litespec/backend/persistence#collect-events-without-a-public-unit-of-work` | `event`, `limit`, and `runbook` | A committed change requires delivery that cannot be lost. |
| [efcore](https://litespec.dev/2.0.0/backend/dotnet/ext/efcore.md) | `local` | The persistence and dependency provisions its Baseline relationship section names | None | Selected aggregates require relational persistence instead of Marten. |
| [realtime](https://litespec.dev/2.0.0/ext/realtime.md) | `local` | None | `event`, `limit` | Polling cannot meet a measured update-latency requirement. |
| [report](https://litespec.dev/2.0.0/ext/report.md) | `local` | None | `limit` | Complex reports or large exports exceed normal request reads. |
| [jobs](https://litespec.dev/2.0.0/ext/jobs.md) | `local` | None | `limit`, `runbook` | Behavior requires recurring, delayed, or calendar-based Worker work. |
| [site](https://litespec.dev/2.0.0/ext/site.md) | `project` | None | None | The product ships a public static website beside its application. |
| [stage](https://litespec.dev/2.0.0/ext/stage.md) | `project` | None | None | The first deployment holds no customer data yet, or a past promotion goes on record. |
| [delegation](https://litespec.dev/2.0.0/ext/delegation.md) | `project` | None | None | One agent starts another agent on the same tree. |

The manifest is the machine-readable source for `activationScope`, `replaces`, and `switchesOn`. This table explains the selection decision.

## Switched-on types

`switchesOn` names the record types a selection requires. Selecting the outbox requires Event and Limit records, so a project that selects it writes both. A type the project already requires stays required.

## Activation

`litespec/core/scope#select-conditional-extensions-explicitly` states when an extension activates. `litespec/core/scope#record-selected-extensions` states where it is listed. `litespec/core/scope#record-selected-extensions` requires the project record.

The [agent protocol](https://litespec.dev/2.0.0/core/agent.md) carries the ordered steps an agent follows.

## Example

The project selects both `locale` and `outbox`, each with the criterion it met and a review date:

```json
{
  "selectedExtensions": [
    { "id": "locale", "criterion": "The product ships in English and Dutch.", "reviewBy": "2027-03-01" },
    { "id": "outbox", "criterion": "Shipment dispatch cannot lose a delivery.", "reviewBy": "2027-03-01" }
  ]
}
```

`litespec/core/scope#select-conditional-extensions-explicitly` requires that an extension is selected only when its criteria apply. The object form records which criterion that was. The consumer validator reports a selection whose `reviewBy` has passed. A selection that costs nothing to keep is a selection no one removes.