How to add a custom metric formatter¶

This guide shows you how to add a new wire format for the @@metrics endpoint, alongside the built-in Prometheus text and JSON formats.

A formatter is a named utility implementing IMetricFormatter. The utility name becomes the value of the format query-string parameter. For the interface members, see Interfaces.

Implement the formatter¶

from zope.interface import implementer
from plone.observability.interfaces import IMetricFormatter


@implementer(IMetricFormatter)
class CSVFormatter:
    content_type = "text/csv"

    def format(self, metrics):
        lines = ["name,value,type,scope,help"]
        for m in metrics:
            lines.append(f"{m.name},{m.value},{m.type},{m.scope},{m.help}")
        return "\n".join(lines)

Register the utility¶

<utility
    factory=".formatters.CSVFormatter"
    provides="plone.observability.interfaces.IMetricFormatter"
    name="csv"
    />

Use it¶

Select the format by name with the format query-string parameter.

http://your-plone-host/@@metrics?format=csv