Docs Chain variables in recorder exports

Chain variables in recorder exports

The recorder captures live request/response pairs verbatim. When you
export a session into a script (Postman collection, perf test, test
runner script, or mocks), the captured literals — auth tokens,
order IDs, CSRF values — get baked in. The moment the upstream
service rotates any of them, your generated artefact stops working.

The chain-variables option turns those literals into reusable
variables.

What gets detected

The engine scans every entry’s response for values that show up
later in another entry’s request. Detected sources:

  • JSON keys (any depth: data.user.id, items[0].uuid)
  • Response headers (X-CSRF-Token, X-Trace-Id, …)
  • Set-Cookie name/value pairs
  • URL-shaped headers (Location, Link, Content-Location) — both
    the full URL and each path / query value individually

Detected sinks:

  • URL path segments
  • URL query string values
  • Request headers (including Authorization: Bearer <token> —
    prefix is preserved)
  • Cookies sent back via Cookie:
  • application/x-www-form-urlencoded form fields
  • multipart/form-data text fields (file parts are skipped)
  • JSON request body — scalar values at any depth

How values become variables

The engine matches exact string occurrences (substrings are ignored
to avoid false positives) and synthesises a stable identifier from
the source path:

Source Variable name
response.body.json.user.id user_id
response.body.json.items[0].uuid items_0_uuid
response.header.X-CSRF-Token x_csrf_token
response.set-cookie.session session_cookie
response.header.Location:query.code code

Each consumer location in a later request is rewritten to reference
{{name}} instead of the captured literal.

Numeric values (12345, 987654321) are excluded by default
because they produce noisy correlations (any short integer that
repeats across unrelated endpoints would otherwise produce a
variable). Opt back in with the Include numeric values flag.

Where to flip the switch

In the extension (Mockarty Capture)

On the Actions tab of the extension’s side panel:

☑ Replace correlated values with {{var}}

On by default. It only appears when at least one of the available actions exports a
script. The toggle affects every “Save as …” button at once — Postman collection,
functional test, load script, and mocks.

In the Web UI

The recorder session’s Export menu has a toggle checkbox above the format selector.

Via the API

Append ?variableize=1 to any of:

  • POST /api/v1/recorder/:id/export (HAR)
  • POST /api/v1/recorder/:id/export-postman
  • POST /api/v1/recorder/:id/export-perf
  • POST /api/v1/recorder/:id/export-test
  • POST /api/v1/recorder/:id/mocks

Via the CLI

# Preview the chain rewrite — variables + extract steps, no download.
mockarty-cli recorder variableize <session-id>

# Inspect with options.
mockarty-cli recorder variableize <session-id> \
  --include-numeric --max-vars 32 --entries e1,e2,e3

What ends up in the generated artefacts

Format Inline placeholders Extract / seed wiring
Postman v2.1 {{var}} in URL/header/body pm.collectionVariables.set(...) events on source entries + variable block seeded with captured sample values
Perf script JS template literal: "prefix/" + user_id var name = "<sample>"; declarations at the top + // := comment on source entries pointing at the response path
Test script Same JS template literal var name = r1.body.x; extraction one-liners after source entries
Mocks {{var}} in http.route / request body / headers (no extract step — mocks consume the variable at runtime)
HAR {{var}} in consumer request URL/body/headers Sidecar via the X-Mockarty-Variables response header ({variables, extracts} JSON)

Limitations

  • Variables are only inferred from previous responses; cross-
    branch flows (e.g. one request whose body uses a value from a
    later one) aren’t possible — and shouldn’t be in a real chain.
  • Very short or trivial values (true, null, 42, status codes)
    are filtered out by default.
  • Identical values that appear in multiple unrelated entries get
    one variable; later sources reference the same name.
  • File parts in multipart bodies are not extracted (binary, opaque).
  • Re-running Variableize on already-parameterised output is a
    no-op — no double-substitution.

What to do when nothing got detected

  • Lower the minimum value length via the API (minValueLength)
    — the default is 4 chars.
  • Toggle Include numeric values if your flow uses bare integer
    IDs without any string prefix.
  • Double-check the captured response actually contains the value
    the next request consumes. Network proxies sometimes strip
    request bodies; the recorder reports the bytes it saw.
Previous
Chaos Engineering