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Handoff

handoff writes a block for each failing and each slowest request with what a backend engineer needs to find it in their own logs: the time in UTC, the correlation ids, the server address and a masked curl command. Send them the blocks and not the capture.

wiretrail checkout.har handoff --filter "path:/v1/cart/sync" --top 1

# e000069 [503] POST api.shop.example/v1/cart/sync
  time: 2026-10-20T09:14:27+00:00 (+25000ms)
  correlation: req_fa6f840121, e1e598c1a6e1ae1d-AMS
  server ip: 203.0.113.30
  curl -X POST 'https://api.shop.example/v1/cart/sync' \
    -H 'accept: application/json, text/plain, */*' \
    -H 'accept-encoding: gzip, deflate, br' \
    -H 'user-agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36' \
    -H 'origin: https://shop.example' \
    -H 'referer: https://shop.example/' \
    -H 'authorization: <redacted>' \
    -H 'x-app-version: 4.12.0' \
    -H 'content-type: application/json' \
    -H 'content-length: 48' \
    --data '{"cart":"c_55d1","items":[{"qty":1,"sku":1042}]}'

Which requests get a block

Every request that is an error (4xx, 5xx or no status), plus the --top slowest requests, in time order. --top counts the slowest requests to add. It does not cap the number of errors. In this capture 16 requests failed, and --top 3 gives 18 blocks, because two of the three slowest did not fail:

wiretrail checkout.har handoff --top 3 | grep -c '^# e'

18

--filter narrows both sets, so --filter "path:/v1/cart/sync" --top 1 gives every failure on that route and the slowest one among them. Without --top 1 it adds the ten slowest requests of the filtered set.

Read a block

Line Meaning
# e000069 [503] POST api.shop.example/v1/cart/sync The entry id, status, method and route.
time: The start of the request in UTC, and its offset in milliseconds from the start of the capture.
correlation: The correlation ids from the response, the same as errors shows.
server ip: The address that answered, when the capture has it.
the curl command A masked replay, indented.

The time is exact to the millisecond when the request started on a fractional second and is otherwise shown to the second. correlation and server ip are what let the other team look in the right log and find the right machine.

JSON

wiretrail checkout.har handoff --filter "path:/v1/cart/sync" --top 1 --json | jq '.result.items[0] | del(.curl)'

{
  "id": "e000069",
  "method": "POST",
  "host": "api.shop.example",
  "norm_path": "/v1/cart/sync",
  "status": 503,
  "timestamp": "2026-10-20T09:14:27+00:00",
  "offset_ms": 25000.0,
  "correlation_ids": [
    "req_fa6f840121",
    "e1e598c1a6e1ae1d-AMS"
  ],
  "server_ip": "203.0.113.30"
}

The curl field, left out here, holds the command as one string.

Exit code

handoff exits 1 when it writes at least one block and 0 when it writes none.