---
title: CEL functions and operators
description: Reference for functions and operators available in CEL expressions used to evaluate Telegraf agent status.
url: https://docs.influxdata.com/telegraf/controller/reference/agent-status-eval/functions/
estimated_tokens: 3102
product: Telegraf
version: v1
---

# CEL functions and operators

#### Telegraf Controller is in Public Beta

Telegraf Controller is in public beta and will be part of the future Telegraf Enterprise offering. While in beta, Telegraf Controller is **not meant for production use**. The Telegraf Controller documentation is a work in progress, and we are actively working to improve it. If you have any questions or suggestions, please [submit an issue](https://github.com/influxdata/docs-v2/issues/new?labels=Telegraf%20Controller). We welcome any and all contributions.

Beta expectations

-   **No configuration or agent limits**  
    While in beta, Telegraf Controller doesn't place any limits on the number of configurations you can store or the number of Telegraf agents you can track. However, upon being generally available, the free distribution of Telegraf Controller will have limits introduced, with the option to increase limits through a Telegraf Enterprise license.
-   **Potential breaking changes**  
    While in beta, we will do our best to no longer make breaking changes to Telegraf Controller, however, they may be necessary. The majority of changes we make will be additive and non-breaking, and include any necessary migrations. When we do need to make breaking changes, we will do our best to communicate them clearly and in advance to minimize disruption.
-   **Flexible release schedule**  
    While in beta, we will continue to create new releases of Telegraf Controller, but likely at irregular intervals. We will provide [Telegraf Controller release notes](/telegraf/controller/reference/release-notes/) to make it easy to track updates.

Provide beta feedback

-   Use the **Feedback** feature in the Telegraf Controller UI.
-   [Join the InfluxDB Community Slack](https://influxdata.com/slack) and post feedback in the **#telegraf-enterprise-alpha** channel.
-   Post feedback in the [InfluxData Community](https://community.influxdata.com).

Join our public channels

-   [InfluxDB Community Slack *(Preferred)*](https://influxdata.com/slack)
-   [InfluxData Community](https://community.influxdata.com)
-   [InfluxDB Subreddit](https://reddit.com/r/influxdb)

CEL expressions for agent status evaluation support built-in CEL operators and the following function libraries.

## Time functions

### `now()`

Returns the current time. Use with `last_update` to calculate durations or detect stale data.

```js
// True if more than 10 minutes since last heartbeat
now() - last_update > duration('10m')
```

```js
// True if more than 5 minutes since last heartbeat
now() - last_update > duration('5m')
```

## Math functions

Math functions from the [CEL math library](https://github.com/google/cel-go/blob/master/ext/README.md#math) are available for numeric calculations.

### Commonly used functions

| Function | Description | Example |
| --- | --- | --- |
| math.greatest(a, b, ...) | Returns the greatest value. | math.greatest(log_errors, log_warnings) |
| math.least(a, b, ...) | Returns the least value. | math.least(agent.metrics_gathered, 1000) |

### Example

```js
// Warn if either errors or warnings exceed a threshold
math.greatest(log_errors, log_warnings) > 5
```

## String functions

String functions from the [CEL strings library](https://github.com/google/cel-go/blob/master/ext/README.md#strings) are available for string operations. These are useful when checking plugin `alias` or `id` fields.

### Example

```js
// Check if any input plugin has an alias containing "critical"
inputs.cpu.exists(i, has(i.alias) && i.alias.contains("critical"))
```

## Encoding functions

Encoding functions from the [CEL encoder library](https://github.com/google/cel-go/blob/master/ext/README.md#encoders) are available for encoding and decoding values.

## Operators

CEL supports standard operators for building expressions.

### Comparison operators

| Operator | Description | Example |
| --- | --- | --- |
| == | Equal | metrics == 0 |
| != | Not equal | log_errors != 0 |
| < | Less than | agent.metrics_gathered < 100 |
| <= | Less than or equal | buffer_fullness <= 0.5 |
| > | Greater than | log_errors > 10 |
| >= | Greater than or equal | metrics >= 1000 |

### Logical operators

| Operator | Description | Example |
| --- | --- | --- |
| && | Logical AND | log_errors > 0 && metrics == 0 |
| || | Logical OR | log_errors > 10 || log_warnings > 50 |
| ! | Logical NOT | !(metrics > 0) |

### Arithmetic operators

| Operator | Description | Example |
| --- | --- | --- |
| + | Addition | log_errors + log_warnings |
| - | Subtraction | agent.metrics_gathered - agent.metrics_dropped |
| * | Multiplication | log_errors * 2 |
| / | Division | agent.metrics_dropped / agent.metrics_gathered |
| % | Modulo | metrics % 100 |

### Ternary operator

```js
// Conditional expression
log_errors > 10 ? true : false
```

### List operations

| Function | Description | Example |
| --- | --- | --- |
| exists(var, condition) | True if any element matches. | inputs.cpu.exists(i, i.errors > 0) |
| all(var, condition) | True if all elements match. | outputs.influxdb_v2.all(o, o.errors == 0) |
| size() | Number of elements. | inputs.cpu.size() > 0 |
| has() | True if a field or key exists. | has(inputs.cpu) |