> ## Documentation Index
> Fetch the complete documentation index at: https://docs.withfoundry.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Memory Engine overview

> Persistent AI context API with pgvector semantic search.

# Memory Engine overview

The Memory Engine stores and retrieves **semantic context** for your app. Content is embedded, indexed with pgvector, and queried by meaning—so you can inject relevant past context into prompts without keyword hacks.

## Concepts

| Concept       | Description                                                                              |
| ------------- | ---------------------------------------------------------------------------------------- |
| **Namespace** | Isolates memories per app or tenant (e.g. `my-app`, `user-123`). Required on every call. |
| **Entry**     | One unit of memory: `content` (text), optional `metadata` (JSON). Stored and embedded.   |
| **Search**    | Semantic search over a namespace. Returns entries ranked by similarity to the query.     |
| **Context**   | Pre-built context string from search results, ready to paste into an LLM prompt.         |

## Flow

1. **Write** — Send entries (and optional metadata) via the API or SDK. Foundry embeds and indexes them.
2. **Search** — Query by natural language; get back the most relevant entries.
3. **Context** — Call the context endpoint to get a single string you can inject into a system or user message.

## Limits and quotas

* **Payload size**: Max request body and per-entry content length follow your plan (see dashboard).
* **Namespaces**: No hard limit; use one per app or per user for isolation.
* **Rate limits**: Applied per API key; 429 responses include `Retry-After`.

## Next steps

<CardGroup cols={3}>
  <Card title="Write memories" icon="pen" href="/memory/write">
    Write single or batch entries with metadata.
  </Card>

  <Card title="Search" icon="magnifying-glass" href="/memory/search">
    Semantic search and ranking.
  </Card>

  <Card title="Context" icon="message" href="/memory/context">
    Build context strings for LLM prompts.
  </Card>
</CardGroup>