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

# Transforms

> Modify data in-flight — filter, redact PII, reduce duplicates, and extract log patterns.

Transforms modify events and logs as they flow through the pipeline. You can drop unwanted data, scrub PII, consolidate duplicates, and extract patterns from logs — all before data reaches your sinks.

Transforms are chained in order within a routing rule. Each one receives a batch, modifies it, and passes it to the next.

## Available transforms

| Transform                               | What it does                     | Use when…                                                            |
| --------------------------------------- | -------------------------------- | -------------------------------------------------------------------- |
| [Filter](/pipeline/transforms/filter)   | Drop or keep events by condition | You want to exclude health checks, debug logs, or internal traffic   |
| [Redact](/pipeline/transforms/redact)   | Remove or pseudonymize PII       | You need GDPR compliance or want to scrub emails, IPs, phone numbers |
| [Reduce](/pipeline/transforms/reduce)   | Consolidate duplicate events     | Error storms or repeated events are inflating your volume            |
| [Pattern](/pipeline/transforms/pattern) | Extract log patterns with Drain  | You want to cluster similar log messages for anomaly detection       |

## Configuration

Add transforms to any routing rule in your `tell.toml`:

```toml theme={null}
[[routing.rules]]
match = { source = "app" }
sinks = ["analytics"]

[[routing.rules.transformers]]
type = "filter"
action = "drop"
field = "path"
operator = "eq"
value = "/health"

[[routing.rules.transformers]]
type = "redact"
strategy = "hash"
hash_key = "your-secret-key"
patterns = ["email", "ipv4"]
scan_all = true
```

Transforms run in the order listed. In this example, health check events are dropped first, then PII is hashed in the remaining events.

## What's next

* [Filter](/pipeline/transforms/filter) — drop or keep events by condition
* [Redact](/pipeline/transforms/redact) — scrub PII with 11 built-in patterns
* [Reduce](/pipeline/transforms/reduce) — consolidate duplicate events
* [Pattern](/pipeline/transforms/pattern) — extract log patterns
* [Routing](/pipeline/routing) — how transforms fit into routing rules