--- title: "Types and values | Grafana Agent documentation" description: "Learn about the River types and values" --- > For a curated documentation index, see [llms.txt](/llms.txt). For the complete documentation index, see [llms-full.txt](/llms-full.txt). # Types and values River uses the following types for its values: - `number`: Any numeric value, like `3` or `3.14`. - `string`: A sequence of Unicode characters representing text, like `"Hello, world!"`. - `bool`: A boolean value, either `true` or `false`. - `array`: A sequence of values, like `[1, 2, 3]`. Elements within the list are indexed by whole numbers, starting with zero. - `object`: A group of values identified by named labels, like `{ name = "John" }`. - `function`: A value representing a routine that runs with arguments to compute another value, like `env("HOME")`. Functions take zero or more arguments as input and always return a single value as output. - `null`: A type that has no value. ## Naming convention In addition to the preceding types, the \[component reference]\[] documentation uses the following conventions for referring to types: - `any`: A value of any type. - `map(T)`: an `object` with the value type `T`. For example, `map(string)` is an object where all the values are strings. The key type of an object is always a string or an identifier converted into a string. - `list(T)`: an `array` with the value type`T`. For example, `list(string)` is an array where all the values are strings. - `duration`: a `string` denoting a duration of time, such as `"1d"`, `"1h30m"`, `"10s"`. Valid units are: - `d` for days. - `h` for hours. - `m` for minutes. - `s` for seconds. - `ms` for milliseconds. - `ns` for nanoseconds. You can combine values of descending units to add their values together. For example, `"1h30m"` is the same as `"90m"`. ## Numbers River handles integers, unsigned integers, and floating-point values as a single ’number’ type, simplifying writing and reading River configuration files. Alloy ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy ```alloy 3 == 3.00 // true 5.0 == (10 / 2) // true 1e+2 == 100 // true 2e-3 == 0.002 // true ``` ## Strings Strings are represented by sequences of Unicode characters surrounded by double quotes `""`. Alloy ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy ```alloy "Hello, world!" ``` A `\` in a string starts an escape sequence to represent a special character. The following table shows the supported escape sequences. Expand table | Sequence | Replacement | |--------------|-----------------------------------------------------------------------------------------| | `\\` | The `\` character `U+005C` | | `\a` | The alert or bell character `U+0007` | | `\b` | The backspace character `U+0008` | | `\f` | The formfeed character `U+000C` | | `\n` | The newline character `U+000A` | | `\r` | The carriage return character `U+000D` | | `\t` | The horizontal tab character `U+0009` | | `\v` | The vertical tab character `U+000B` | | `\'` | The `'` character `U+0027` | | `\"` | The `"` character `U+0022`, which prevents terminating the string | | `\NNN` | A literal byte (NNN is three octal digits) | | `\xNN` | A literal byte (NN is two hexadecimal digits) | | `\uNNNN` | A Unicode character from the basic multilingual plane (NNNN is four hexadecimal digits) | | `\UNNNNNNNN` | A Unicode character from supplementary planes (NNNNNNNN is eight hexadecimal digits) | ## Raw strings Raw strings are represented by sequences of Unicode characters surrounded by backticks ``` `` ```. Raw strings don’t support any escape sequences. Alloy ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy ```alloy `Hello, "world"!` ``` Within the backticks, any character may appear except a backtick. You can include a backtick by concatenating a double-quoted string that contains a backtick using `+`. A multiline raw string is interpreted exactly as written. Alloy ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy ```alloy `Hello, "world"!` ``` The preceding multiline raw string is interpreted as a string with the following value. string ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy ```string Hello, "world"! ``` ## Bools Bools are represented by the symbols `true` and `false`. ## Arrays You construct arrays with a sequence of comma-separated values surrounded by square brackets `[]`. Alloy ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy ```alloy [0, 1, 2, 3] ``` You can place values in array elements on separate lines for readability. A comma after the final value must be present if the closing bracket `]` is on a different line than the final value. Alloy ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy ```alloy [ 0, 1, 2, ] ``` ## Objects You construct objects with a sequence of comma-separated key-value pairs surrounded by curly braces `{}`. Alloy ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy ```alloy { first_name = "John", last_name = "Doe", } ``` You can omit the comma after the final key-value pair if the closing curly brace `}` is on the same line as the final pair. Alloy ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy ```alloy { name = "John" } ``` If the key isn’t a valid identifier, you must wrap it in double quotes like a string. Alloy ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy ```alloy { "app.kubernetes.io/name" = "mysql", "app.kubernetes.io/instance" = "mysql-abcxyz", namespace = "default", } ``` > Note > > Don’t confuse objects with blocks. > > - An *object* is a value assigned to an [Attribute](../../syntax/#attributes). You **must** use commas between key-value pairs on separate lines. > - A [Block](../../syntax/#blocks) is a named structural element composed of multiple attributes. You **must not** use commas between attributes. ## Functions You can’t construct function values. You can call functions from the standard library or export them from a component. ## Null The null value is represented by the symbol `null`. ## Special types #### Secrets A `secret` is a special type of string that’s never displayed to the user. You can assign `string` values to an attribute expecting a `secret`, but never the inverse. It’s impossible to convert a secret to a string or assign a secret to an attribute expecting a string. #### Capsules A `capsule` is a special type that represents a category of *internal* types used by Grafana Agent Flow. Each capsule type has a unique name and is represented to the user as `capsule("")`. You can’t construct capsule values. You can use capsules in expressions as any other type. Capsules aren’t inter-compatible, and an attribute expecting a capsule can only be given a capsule of the same internal type. If an attribute expects a `capsule("prometheus.Receiver")`, you can only assign a `capsule("prometheus.Receiver")` type. The specific type of capsule expected is explicitly documented for any component that uses or exports them. In the following example, the `prometheus.remote_write` component exports a `receiver`, which is a `capsule("prometheus.Receiver")` type. You can use this capsule in the `forward_to` attribute of `prometheus.scrape`, which expects an array of `capsule("prometheus.Receiver")`. Alloy ![Copy code to clipboard](/media/images/icons/icon-copy-small-2.svg) Copy ```alloy prometheus.remote_write "default" { endpoint { url = "http://localhost:9090/api/v1/write" } } prometheus.scrape "default" { targets = [/* ... */] forward_to = [prometheus.remote_write.default.receiver] } ```