Determinism — what is and isn’t

Not everything in API testing can be deterministic. Here’s how DevTools frames it so expectations match reality.

Engine behavior (deterministic)

• Execution ordering for a given flow definition
• Report formats and exit codes (CLI)

Mapping behavior (rule‑based, repeatable)

• Variable mapping uses stable, repeatable rules
• Rules can be overridden per step when payloads change
• Heuristics prefer explicit selectors over fuzzy matches

Traffic reality (not deterministic)

• Payload shape changes, nonce values, and timestamps
• Server‑side ordering or fan‑out behavior
• External rate limiting and backpressure

Recommended practices

• Prefer explicit JSONPath selectors for mapping critical values
• Add assertions at flow and step boundaries to catch drift early
• Gate non‑critical steps with soft assertions or retries
• Use environment variables for ephemeral tokens and rotate via CI secrets

See also

• Variable mapping system: /docs/how-to/environments-and-variables#variable-mapping-system
• Assertions and gates: /docs/how-to/working-with-flows#assertions-and-validations