---
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: 1401
publisher: InfluxData
canonical: https://docs.influxdata.com/telegraf/controller/reference/agent-status-eval/functions/
date: '2026-03-26T08:20:04-06:00'
lastmod: '2026-03-26T08:20:04-06:00'
---

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)`             |
| Function | Description | Example |
| --- | --- | --- |
| 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) |

| Operator | Description | Example |
| --- | --- | --- |
| 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 |

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

| Operator | Description | Example |
| --- | --- | --- |
| 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 |

| Function | Description | Example |
| --- | --- | --- |
| 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) |