---
title: Expressions
description: Write expressions that match request characteristics for rule evaluation.
image: https://developers.cloudflare.com/core-services-preview.png
---

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# Expressions

The Rules language supports two kinds of expressions: simple and compound.

## Simple expressions

**Simple expressions** compare a value from an HTTP request to a value defined in the expression. For example, this simple expression matches Microsoft Exchange Autodiscover requests:

```
http.request.uri.path matches "/autodiscover\.(xml|src)$"
```

Simple expressions have the following syntax:

```
<field> <comparison_operator> <value>
```

Where:

* [Fields](https://developers.cloudflare.com/ruleset-engine/rules-language/fields/) specify properties associated with an HTTP request.
* [Comparison operators](https://developers.cloudflare.com/ruleset-engine/rules-language/operators/#comparison-operators) define how values must relate to actual request data for an expression to return `true`.
* [Values](https://developers.cloudflare.com/ruleset-engine/rules-language/values/) represent the data associated with fields. When evaluating a rule, Cloudflare compares these values with the actual data obtained from the request.

## Compound expressions

**Compound expressions** use [logical operators](https://developers.cloudflare.com/ruleset-engine/rules-language/operators/#logical-operators) such as `and` to combine two or more expressions into a single expression.

For example, this expression uses the `and` operator to target requests to `www.example.com` that are not on ports 80 or 443:

```
http.host eq "www.example.com" and not cf.edge.server_port in {80 443}
```

Compound expressions have the following general syntax:

```
<expression> <logical_operator> <expression>
```

Compound expressions allow you to generate sophisticated, highly targeted rules.

## Maximum rule expression length

The maximum length of a rule expression is 4,096 characters.

This limit applies whether you use the visual [Expression Builder](https://developers.cloudflare.com/ruleset-engine/rules-language/expressions/edit-expressions/#expression-builder) to define your expression, or write the expression manually in the [Expression Editor](https://developers.cloudflare.com/ruleset-engine/rules-language/expressions/edit-expressions/#expression-editor).

## Maximum regular expressions per rule

Each rule can contain a maximum of 64 regular expressions in its expression. This limit applies across all rule types that use the [Rules language](https://developers.cloudflare.com/ruleset-engine/rules-language/).

Rules that exceed this limit cannot be created or updated. Existing rules above this limit continue to work but cannot be modified until the expression is simplified.

## Additional features

You can also use the following Rules language features in your expressions:

* [Grouping symbols](https://developers.cloudflare.com/ruleset-engine/rules-language/operators/#grouping-symbols) allow you to explicitly group expressions that should be evaluated together.
* [Functions](https://developers.cloudflare.com/ruleset-engine/rules-language/functions/) allow you to manipulate and validate values in expressions.

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