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What varies between calls

diff answers "these calls look identical, so what is different?" For every endpoint that was called at least twice, it lists the query parameters, the request headers and the body that change between calls. It is how you tell a call that is truly redundant from one that only looks that way.

wiretrail checkout.har diff

POST api.shop.example/v1/session/ping  (12 calls, body: volatile-only)

GET search.shop.example/v1/suggest  (12 calls, body: none)
  query q varies: r, ru, run
  headers vary: x-device-token

GET api.shop.example/v1/flags  (6 calls, body: none)
  query cb varies: 1792487642, 1792487649, 1792487656

What it compares

Calls are grouped by method, host and normalized path, not by query. So one group holds calls with different query strings, and the group shows which keys differ. Only groups with some variation are listed.

Line Meaning
12 calls Calls in the group.
query q varies: r, ru, run The query key that differs, with up to the first three distinct values. Sensitive values are masked.
headers vary: x-device-token Request header names whose value differs between calls, including calls that lack the header. Names are lower case.
body: volatile-only The body verdict, below.

Body verdicts

Verdict Meaning
none Fewer than two calls have a request body.
identical Every body is the same text.
volatile-only The bodies are JSON objects, and only keys that name a timestamp, nonce, date, cache-buster or request id differ.
meaningful Something else differs, or the bodies are not JSON objects.

A key counts as volatile when its lower-case name equals or contains any of timestamp, ts, nonce, date, cb, cachebuster, requestid, request_id or _.

The volatile test is broad

The list includes _ and ts, and the test is a substring test. So any key with an underscore, such as order_id, and any key that ends in ts, such as events, results or points, counts as volatile. Two orders that differ only in those keys get volatile-only:

wiretrail quirks/volatile-substring.har diff


POST api.test.example/v1/orders  (2 calls, body: volatile-only)

Those two calls place different orders, and the verdict does not show it. Treat volatile-only as "worth checking", not "proved redundant", and read the bodies with extract or show-entry. Limitations lists this.

Read a result

The heartbeat is volatile-only: only a key named ts changes. Which key, and what it holds:

wiretrail checkout.har extract '$.ts' --target req --filter "path:/v1/session/ping" --top 3

e000038  1792487648000
e000041  1792487649500
e000042  1792487651000

The timestamp is 1.5 seconds apart each time, and nothing else is different. The calls are redundant apart from the clock, so removing them loses no information. Remove redundant calls does it.

An endpoint whose calls differ only in the id in the path shows nothing. The twelve price calls are identical once ids are normalized, so diff prints an empty list for them:

wiretrail checkout.har diff --filter "path:/v1/products/*/price"

== wiretrail diff ==

Empty output means nothing varies in query, headers or body. It does not say the calls are the same request. Look at the path ids with duplicates or timeline.

When a header varies

A varying authorization header is worth noticing. It shows that a token changed between calls:

GET api.shop.example/v1/cart  (4 calls, body: none)
  headers vary: authorization

GET api.shop.example/v1/products  (4 calls, body: none)
  query page varies: 1, 2, 3

The cart calls span the expired token and its replacement. Auth failures and refresh reads that.

JSON

wiretrail checkout.har diff --filter "path:/v1/session/ping" --json | jq '.result.groups[0] | del(.entry_ids)'

{
  "host": "api.shop.example",
  "method": "POST",
  "norm_path": "/v1/session/ping",
  "count": 12,
  "varying_query": [],
  "varying_header_names": [],
  "body_verdict": "volatile-only"
}

Exit code

diff exits 1 when any group has a meaningful body or a varying authorization header, and 0 otherwise. A heartbeat that is volatile-only exits 0:

wiretrail checkout.har diff --filter "path:/v1/session/ping" > /dev/null; echo "exit code: $?"

exit code: 0