Custom Levels

Logly supports custom log levels with full control over name, numeric severity, ANSI color, and icon/emoji.

Built-in Levels

Level	Number	Color
TRACE	5	dim
DEBUG	10	blue
INFO	20	-
NOTICE	25	cyan
SUCCESS	30	green
WARNING	40	yellow
ERROR	50	red
FAIL	55	magenta
CRITICAL	60	bold_red
FATAL	70	bold_red

Register a Custom Level

from logly import logger

logger.level("VERBOSE", no=15, color="cyan", icon=">")

Parameters:

• name – Level name (e.g. "VERBOSE", "HTTP", "SECURITY")
• no – Numeric severity (must be unique)
• color – ANSI color name (e.g. "green", "bold_red", "#ff0000")
• icon – Optional icon/emoji displayed in formatted output

Inspect a Level

from logly import logger

info = logger.level("INFO")
print(info.name)  # "INFO"
print(info.no)  # 20
print(info.color)  # None
print(info.icon)  # None

Returns a Level object with .name, .no, .color, .icon attributes.

Log with Custom Level

from logly import logger

logger.level("METRIC", no=28, color="magenta", icon="#")

logger.log("METRIC", "request latency 42ms")

Use Icon in Format Strings

from logly import logger

logger.level("HTTP", no=21, color="blue", icon=">")

sink_id = logger.add(
    lambda msg: print(msg, end=""),
    format="{level_icon} {level} | {message}",
    level="TRACE",
)

logger.log("HTTP", "GET /api/users")
logger.info("Application started")

logger.remove(sink_id)

Output:

> HTTP | GET /api/users
 INFO | Application started

Available format tokens:

Token	Description
{level}	Level name
{level_no}	Numeric priority
{level_icon}	Level icon/emoji
{message}	Log message
{time}	Timestamp
{name}	Logger name
{file}	Source file
{line}	Line number
{function}	Function name

Register Multiple Custom Levels

from logly import logger

CUSTOM_LEVELS = [
    ("HTTP", 21, "blue", ">"),
    ("DATABASE", 22, "magenta", "*"),
    ("SECURITY", 35, "red", "!"),
    ("METRIC", 28, "cyan", "#"),
]

for name, no, color, icon in CUSTOM_LEVELS:
    logger.level(name, no=no, color=color, icon=icon)

logger.log("HTTP", "GET /api/users")
logger.log("DATABASE", "Connected to PostgreSQL")
logger.log("SECURITY", "Authentication failed")
logger.log("METRIC", "request latency 42ms")

Modify Existing Levels

from logly import logger

# Change the color of an existing level
logger.level("INFO", no=20, color="bold_green", icon="i")

# Verify the change
info = logger.level("INFO")
print(info.color)  # "bold_green"
print(info.icon)  # "i"

List All Registered Levels

from logly import list_levels

levels = list_levels()
print(levels)
# ["TRACE", "DEBUG", "INFO", "NOTICE", "SUCCESS", "WARNING", "ERROR", "FAIL", "CRITICAL", "FATAL", "HTTP", ...]

Level Class Reference

from logly import Level

# Level is a frozen dataclass
info = logger.level("INFO")
assert isinstance(info, Level)

# Access properties
assert info.name == "INFO"
assert info.no == 20
assert info.color is None
assert info.icon is None