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

# Filters

> Narrow retrieval candidates by metadata — tag, source, date, entity.

Filters run **before** ranking. They cut the candidate pool down to only chunks matching the criteria, so ranking works on a focused set.

## What you can filter on

Every enriched chunk carries metadata. Common filterable fields:

* **Tags** — any tag added by the Auto-tag enricher.
* **Source** — which document, folder, or database row.
* **Path** — heading path or folder location.
* **Language** — the chunk's detected language.
* **Entities** — extracted people, orgs, products.
* **Modified date** — when the source was last updated.
* **Custom fields** — anything an inline enricher wrote.

Add fields via the [Enrich stage](/build/foundry/enrich).

## Filter expressions

Filters are expressed as JSON-ish predicates. Examples:

```json theme={null}
{ "tag": "billing" }
```

```json theme={null}
{ "tag": { "$in": ["billing", "pricing"] } }
```

```json theme={null}
{ "modified_at": { "$gte": "2026-01-01" } }
```

```json theme={null}
{ "$and": [
  { "tag": "customer-facing" },
  { "language": "en" },
  { "not": { "tag": "deprecated" } }
] }
```

Operators: `$eq`, `$ne`, `$in`, `$nin`, `$gt`, `$gte`, `$lt`, `$lte`, `$contains`, `$startsWith`, `$exists`, `$and`, `$or`, `$not`.

## Filters at three levels

Filters compose across levels. Anything set at a higher level applies to all lower ones.

1. **Data source level** — attached to a document collection. Applies to every query against it.
2. **Preset level** — inside a Retrieval preset. Applies to every Agent using the preset.
3. **Query level** — set per-call, at runtime. Set by the Agent via a special tool argument, or by your code.

Runtime filters merge into preset filters (both must match). This lets an Agent narrow further without exposing "you can only search customer-facing docs" as a system rule.

## Dynamic filters from variables

Filters can reference Flow variables:

```json theme={null}
{ "department": "{vars.CURRENT_USER_DEPT}" }
```

Common pattern: per-tenant scoping. Set the variable at run start with the requester's tenant ID, and every retrieval is automatically scoped.

## Testing

The preset **Test** panel lets you set a runtime filter and see how it changes the results. Great for validating access control before shipping.

## Performance

Filters on indexed fields (tag, source, date) are free — they run at index scan time. Filters on unindexed custom fields degrade to a post-fetch scan and get slower with collection size. Add an index on hot filter fields via the collection settings.