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A tool to scrape a Prometheus client and dump the result as JSON.


(Pre-)historically, Prometheus clients were able to expose metrics as
JSON. For various reasons, the JSON exposition format was deprecated.

Usually, scraping of a Prometheus client is done by the Prometheus
server, which preferably happens with the protocol buffer
format. Sometimes, a human being needs to inspect what a Prometheus
clients exposes. In that case, the text format is used (which is
otherwise meant to allow simplistic clients like shell scripts to
expose metrics to a Prometheus server).

However, some users wish to scrape Prometheus clients with programs
other than the Prometheus server. Those programs would usually use the
protocol buffer format, but for small ad hoc programs, that is too
much of an (programming) overhead. JSON comes in handy for these
use-cases, as many languages offer tooling for JSON parsing.

To avoid maintaining a JSON format in all client libraries, the
prom2json tool has been created, which scrapes a Prometheus client
in protocol buffer or text format and dumps the result as JSON to


Installing and building:

$ go get


$ prom2json

Running with TLS client authentication:

$ prom2json --cert=/path/to/certificate --key=/path/to/key

This will dump the JSON to stdout. Note that the dumped JSON is
not using the deprecated JSON format as specified in the
Prometheus exposition format
. The
created JSON uses a format much closer in structure to the protocol
buffer format. It is only used by the prom2json tool and has no
significance elsewhere. See below for a description.

A typical use-case is to pipe the JSON format into a tool like jq to
run a query over it. That looked like the following when the clients
still supported the deprecated JSON format:

$ curl | jq .

Now simply use prom2json instead of curl (and change the query
syntax according to the changed JSON format generated by prom2json):

$ prom2json | jq .

Example query to retrieve the number of metrics in the http_requests_total metric family (only works with the new format):

$ prom2json | jq '.[]|select(.name=="http_requests_total")|.metrics|length'

JSON format

Note that all numbers are encoded as strings. Some parsers want it
that way. Also, Prometheus allows sample values like NaN or +Inf,
which cannot be encoded as JSON numbers.

    "name": "http_request_duration_microseconds",
    "help": "The HTTP request latencies in microseconds.",
    "type": "SUMMARY",
    "metrics": [
        "labels": {
          "method": "get",
          "handler": "prometheus",
          "code": "200"
        "quantiles": {
          "0.99": "67542.292",
          "0.9": "23902.678",
          "0.5": "6865.718"
        "count": "743",
        "sum": "6936936.447000001"
        "labels": {
          "method": "get",
          "handler": "prometheus",
          "code": "400"
        "quantiles": {
          "0.99": "3542.9",
          "0.9": "1202.3",
          "0.5": "1002.8"
        "count": "4",
        "sum": "345.01"
    "name": "roshi_select_call_count",
    "help": "How many select calls have been made.",
    "type": "COUNTER",
    "metrics": [
        "value": "1063110"

Using Docker

You can deploy this tool using the prom/prom2json Docker image.

For example:

docker pull prom/prom2json

docker run --rm -ti prom/prom2json
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