Text formatters

A text formatter is a function that formats a log record into a string. LogTape has four built-in sinks that can take a text formatter:

• console sink
• stream sink
• file sink
• rotating file sink

Of course, you can write your own sinks that take a text formatter.

Built-in text formatters

LogTape provides three built-in text formatters:

Default text formatter

defaultTextFormatter formats a log record into a string with a simple format. It renders the timestamp, the log level, the message, and the prettified values embedded in the message.

It formats log records like this:

2023-11-14 22:13:20.000 +00:00 [INF] category·subcategory: Hello, world!

ANSI color formatter

This API is available since LogTape 0.5.0.

ansiColorFormatter formats a log record into a string with a simple format and ANSI colors. It renders the timestamp, the log level, the message, and the prettified values embedded in the message.

It formats log records like this:

2025-06-12 10:34:10.465 +00 INF logtape·meta: LogTape loggers are configured.  Note that LogTape itself uses the meta logger, which has category [ "logtape", "meta" ].  The meta logger purposes to log internal errors such as sink exceptions.  If you are seeing this message, the meta logger is automatically configured.  It's recommended to configure the meta logger with a separate sink so that you can easily notice if logging itself fails or is misconfigured.  To turn off this message, configure the meta logger with higher log levels than "info".  See also <https://logtape.org/manual/categories#meta-logger>.
2025-06-12 10:34:10.472 +00 TRC my-app·module: This is a trace log.
2025-06-12 10:34:10.473 +00 DBG my-app·module: This is a debug log with value: { foo: 123 }
2025-06-12 10:34:10.473 +00 INF my-app: This is an informational log.
2025-06-12 10:34:10.474 +00 WRN my-app: This is a warning.
2025-06-12 10:34:10.475 +00 ERR my-app·module: This is an error with exception: Error: This is an exception.
    at file:///tmp/test.ts:28:10
2025-06-12 10:34:10.475 +00 FTL my-app: This is a fatal error.

JSON Lines formatter

This API is available since LogTape 0.11.0.

jsonLinesFormatter formats log records as JSON Lines (also known as Newline-Delimited JSON or NDJSON). Each log record is rendered as a JSON object on a single line, which is a common format for structured logging.

It formats log records like this:

{"@timestamp":"2023-11-14T22:13:20.000Z","level":"INFO","message":"Hello, world!","logger":"my.logger","properties":{"key":"value"}}

Pretty formatter

This API is available since LogTape 1.0.0.

The pretty formatter provides a beautiful, development-friendly console output with colorful icons, smart truncation, and perfect alignment. It's inspired by Signale and specifically designed for local development environments that support true colors and Unicode characters.

To use the pretty formatter, you need to install the @logtape/pretty package:

Deno

deno add jsr:@logtape/pretty

npm

npm add @logtape/pretty

pnpm

pnpm add @logtape/pretty

Yarn

yarn add @logtape/pretty

Bun

bun add @logtape/pretty

The package provides a pre-configured prettyFormatter for immediate use:

import { configure } from "@logtape/logtape";
import { getConsoleSink } from "@logtape/logtape/sink";
import { prettyFormatter } from "@logtape/pretty";

await configure({
  sinks: {
    console: getConsoleSink({ formatter: prettyFormatter }),
  },
  loggers: [
    { category: [], sinks: ["console"], lowestLevel: "debug" },
  ],
});

It formats log records like this:

✨ info    logtape·meta         LogTape loggers are configured.  Note that LogTape itself uses the
                                meta logger, which has category [ 'logtape', 'meta' ].  The meta
                                logger purposes to log internal errors such as sink exceptions.  If
                                you are seeing this message, the meta logger is automatically
                                configured.  It's recommended to configure the meta logger with a
                                separate sink so that you can easily notice if logging itself fails
                                or is misconfigured.  To turn off this message, configure the meta
                                logger with higher log levels than 'info'.  See also
                                <https://logtape.org/manual/categories#meta-logger>.
🔍 trace   myapp·module         This is a trace log.
🐛 debug   myapp·module         This is a debug log with value: { foo: 123 }
✨ info    myapp                This is a very long informational log
⚡ warning myapp                This is a warning.
❌ error   myapp·module         This is an error with exception: Error: This is an exception.
                                    at file:///tmp/test.ts:23:10
💀 fatal   myapp                This is a fatal error.

Configuring text formatters

This API is available since LogTape 0.6.0.

You can customize the built-in text formatters with a TextFormatterOptions or an AnsiColorFormatterOptions object without building a new text formatter from scratch.

Default text formatter

You can customize the default text formatter by calling the getTextFormatter() function with a TextFormatterOptions object. Customizable options include:

timestamp

The timestamp format. This can be one of the following:

• "date-time-timezone": The date and time with the full timezone offset (e.g., 2023-11-14 22:13:20.000 +00:00).
• "date-time-tz": The date and time with the short timezone offset (e.g., 2023-11-14 22:13:20.000 +00).
• "date-time": The date and time without the timezone offset (e.g., 2023-11-14 22:13:20.000).
• "time-timezone": The time with the full timezone offset but without the date (e.g., 22:13:20.000 +00:00).
• "time-tz": The time with the short timezone offset but without the date (e.g., 22:13:20.000 +00).
• "time": The time without the date or timezone offset (e.g., 22:13:20.000).
• "date": The date without the time or timezone offset (e.g., 2023-11-14).
• "rfc3339": The date and time in RFC 3339 format (e.g., 2023-11-14T22:13:20.000Z).
• "none" or "disabled": No display

Alternatively, this can be a function that accepts a timestamp and returns a string.

The default is "date-time-timezone".

level

The log level format. This can be one of the following:

• "ABBR": The log level abbreviation in uppercase (e.g., INF).
• "FULL": The full log level name in uppercase (e.g., INFO).
• "L": The first letter of the log level in uppercase (e.g., I).
• "abbr": The log level abbreviation in lowercase (e.g., inf).
• "full": The full log level name in lowercase (e.g., info).
• "l": The first letter of the log level in lowercase (e.g., i).

Alternatively, this can be a function that accepts a log level and returns a string.

The default is "ABBR".

category

The separator between the category names.

For example, if the separator is "·", the category ["a", "b", "c"] will be formatted as "a·b·c".

The default separator is "·".

If this is a function, it will be called with the category array and should return a string, which will be used for rendering the category.

value

The format of the embedded values.

A function that renders a value to a string. This function is used to render the values in the log record. The default is util.inspect() in Node.js/Bun and Deno.inspect() in Deno.

format

How those formatted parts are concatenated.

A function that formats the log record. This function is called with the formatted values and should return a string. Note that the formatted should not include a newline character at the end.

By default, this is a function that formats the log record as follows:

2023-11-14 22:13:20.000 +00:00 [INF] category·subcategory: Hello, world!

ANSI color formatter

You can customize the ansiColorFormatter by calling the getAnsiColorFormatter() function with an AnsiColorFormatterOptions object. Customizable options include:

timestamp

The timestamp format. The available options are the same as the timestamp option of the default text formatter.

The default is "date-time-tz".

timestampStyle

The ANSI style for the timestamp. "dim" is used by default.

timestampColor

The ANSI color for the timestamp. No color is used by default.

level

The log level format. The available options are the same as the level option of the default text formatter.

The default is "ABBR".

levelStyle

The ANSI style for the log level. "bold" is used by default.

levelColors

The ANSI colors for the log levels. The default colors are as follows:

• "trace": no color (default terminal color)
• "debug": "blue"
• "info": "green"
• "warning": "yellow"
• "error": "red"
• "fatal": "magenta"

category

The separator between the category names. Behaves the same as the category option of the default text formatter.

The default separator is "·".

categoryStyle

The ANSI style for the category. "dim" is used by default.

categoryColor

The ANSI color for the category. No color is used by default.

value

The format of the embedded values. Behaves the same as the value option of the default text formatter.

format

How those formatted parts are concatenated. Behaves the same as the format option of the default text formatter.

Text styles

The timestampStyle, levelStyle, and categoryStyle options can be one of the following:

• "bold"
• "dim"
• "italic"
• "underline"
• "strikethrough"
• null (no style)

Colors

The timestampColor, levelColors (an object with log levels as keys), and categoryColor options can be one of the following:

• "black"
• "red"
• "green"
• "yellow"
• "blue"
• "magenta"
• "cyan"
• "white"
• null (no color)

JSON Lines formatter

This API is available since LogTape 0.11.0.

You can customize the JSON Lines formatter by calling the getJsonLinesFormatter() function with a JsonLinesFormatterOptions object. Customizable options include:

categorySeparator

The separator between category names. For example, if the separator is ".", the category ["a", "b", "c"] will be formatted as "a.b.c".

The default separator is ".".

If this is a function, it will be called with the category array and should return a string or an array of strings, which will be used for rendering the category.

message

The message format. This can be one of the following:

• "template": The raw message template is used as the message.
• "rendered": The message is rendered with the values.

The default is "rendered".

properties

The properties format. This can be one of the following:

• "flatten": The properties are flattened into the root object.
• "prepend:<prefix>": The properties are prepended with the given prefix (e.g., "prepend:ctx_" will prepend ctx_ to each property key).
• "nest:<key>": The properties are nested under the given key (e.g., "nest:properties" will nest the properties under the properties key).

The default is "nest:properties".

Pretty formatter

This API is available since LogTape 1.0.0.

You can customize the pretty formatter by calling the getPrettyFormatter() function with a PrettyFormatterOptions object. This formatter requires the @logtape/pretty package to be installed.

~PrettyFormatterOptions.timestamp

The timestamp format. The available options are the same as the timestamp option of the default text formatter.

The default is "none".

timestampColor

The color for timestamp display. Supports true color RGB values, hex colors, or ANSI color names. Set to null to disable timestamp coloring.

Examples: "#888888", "rgb(128,128,128)", "cyan", null.

The default is "rgb(100,116,139)".

timestampStyle

The visual style applied to timestamp text. Controls text appearance like boldness, dimming, etc. Supports single styles, multiple styles combined, or no styling.

Examples: "dim", "bold", ["bold", "underline"], ["dim", "italic"], null.

The default is "dim".

icons

Icon configuration for each log level. Controls the emoji/symbol displayed before each log entry.

• true: Use built-in emoji set (🔍 trace, 🐛 debug, ✨ info, ⚡ warning, ❌ error, 💀 fatal)
• false: Disable all icons
• Object: Custom icon mapping (e.g., { info: "📘", error: "🔥" })

The default is true.

levelColors

Custom colors for each log level. Allows fine-grained control over level appearance. Each level can have its own color scheme.

Example: { info: "#00ff00", error: "#ff0000", warning: "orange", debug: null }.

The default uses a built-in color scheme.

levelStyle

Visual style applied to log level text. Controls the appearance of the level indicator (e.g., "info", "error").

Examples: "bold", "underline", ["bold", "underline"], null.

The default is "underline".

categorySeparator

Character(s) used to separate category hierarchy levels. Categories are hierarchical and this separator joins them for display.

Examples: "·", ".", ":", " > ", "::".

The default is "·".

categoryWidth

Maximum display width for category names. Controls layout consistency by limiting category width. Long categories are truncated according to categoryTruncate strategy.

The default is 20.

categoryTruncate

Strategy for truncating long category names when they exceed categoryWidth.

• "middle": Keep first and last parts (e.g., "app…middleware")
• "end": Truncate at end (e.g., "app·server·http…")
• false: No truncation

The default is "middle".

categoryColor

Default color for category display. Used as fallback when no specific color is found in categoryColorMap.

The default is "rgb(100,116,139)".

categoryColorMap

Category-specific color mapping based on prefixes. Maps category prefixes (as arrays) to colors for visual grouping. More specific (longer) prefixes take precedence over shorter ones.

Example:

new Map([
  [["app", "auth"], "#ff6b6b"],     // app.auth.* -> red
  [["app", "db"], "#4ecdc4"],       // app.db.* -> teal
  [["app"], "#45b7d1"],             // app.* (fallback) -> blue
])

categoryStyle

Visual style applied to category text.

The default is ["dim", "italic"].

messageColor

Color for log message text content. Does not affect structured values, which use syntax highlighting.

The default is "rgb(148,163,184)".

messageStyle

Visual style applied to log message text.

The default is "dim".

colors

Global color control for the entire formatter. Master switch to enable/disable all color output. When disabled, produces clean monochrome output.

The default is true.

align

Column alignment for consistent visual layout. When enabled, ensures all log components align consistently across multiple log entries.

The default is true.

wordWrap

Text wrapping configuration. When enabled, long messages will be wrapped at the specified width, with continuation lines aligned to the message column.

• true: Auto-detect terminal width
• false: Disable wrapping
• Number: Custom wrap width in columns

The default is true.

inspectOptions

Configuration for structured value inspection and rendering. Controls how objects, arrays, and other complex values are displayed within log messages.

Supported options:

• depth: Maximum depth to traverse when inspecting nested objects
• colors: Whether to use syntax highlighting colors for inspected values
• compact: Whether to use compact formatting for objects and arrays

Pattern-based redaction

This API is available since LogTape 0.10.0.

You can redact sensitive data in log records through pattern-based redaction by wrapping your text formatter with a redactByPattern() function from @logtape/redaction package:

import { getTextFormatter } from "@logtape/logtape";
import {
  EMAIL_ADDRESS_PATTERN,
  JWT_PATTERN,
  redactByPattern,
} from "@logtape/redaction";

const formatter = redactByPattern(getTextFormatter(), [
  EMAIL_ADDRESS_PATTERN,
  JWT_PATTERN,
]);

The above code will create a text formatter that redacts email addresses and JSON Web Tokens (JWTs) in log records. The redactByPattern() function takes a TextFormatter and an array of patterns, and returns a new TextFormatter that redacts the sensitive data matching those patterns.

For more information about it, see the Pattern-based redaction section.

Fully customized text formatter

A text formatter is just a function that takes a log record and returns a string. The type of a text formatter is TextFormatter:

export type TextFormatter = (record: LogRecord) => string;

If you want to build a text formatter from scratch, you can just write a function that takes a log record and returns a string. For example, the following function is a simple text formatter that formats log records into JSON Lines:

function jsonLinesFormatter(record: LogRecord): string {
  return JSON.stringify(record) + "\n";
}

Of course, you can use the built-in getJsonLinesFormatter() function for more sophisticated JSON Lines formatting with customizable options.