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To benchmark REST, WebSockets and webhooks fairly, first define what each timer starts and stops. A REST request’s round-trip duration, a WebSocket event’s delivery age and a webhook’s arrival delay measure different paths; they cannot be ranked as if they were the same “API latency.” This guide lays out a repeatable script design and a result format that makes those differences visible.
What we’re actually measuring
“Latency” can mean elapsed time for a request and response, the age of an event when it arrives, or time spent processing a request after arrival. Name the boundary, direction and clock used for every number. ITU-T’s Recommendation Y.1567 puts it plainly: “All metrics need to be carefully defined.”
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An application-level benchmark measures what the client or receiver experiences, including host and protocol-stack work. That is useful when the question is user-experienced API performance, but it is not a measurement of network-only delay. Y.1567 addresses latency under load and is not a direct comparison of REST, WebSocket and webhook APIs.
- Request latency: time from initiating a request until a defined response boundary, such as receipt of the complete body.
- Delivery latency or event age: time from a provider’s event timestamp to the receiver’s arrival timestamp, when both clocks can be compared reliably.
- Staleness: how old the data is when the application sees it. A short request can return old data; a low event-delivery delay does not tell you how often events arrive.
- Processing time: work performed by your receiver or handler after arrival. Keep it separate from provider-to-receiver delivery.
Which timer belongs to each API pattern?
| Pattern | Useful measurement | Direction and clock | Keep separate |
|---|---|---|---|
| REST | Client request start to headers, or to complete response body—state which. | Round trip measured on the client’s monotonic clock. | Connection setup, body parsing and data freshness unless deliberately included. |
| WebSocket | Connection setup; application message timing; provider event timestamp to local arrival; inter-arrival gaps. | Ping/Pong is an approximate round trip; event age is a one-way estimate across clocks. | Connection setup, Ping/Pong RTT and event delivery age. |
| Webhook | Provider event or attempt timestamp to receiver arrival; optionally receiver processing and acknowledgement time. | Provider-to-receiver one-way estimate across clocks, if timestamps are trustworthy and clocks aligned. | Retry delay, handler work and acknowledgement behavior. |
Build a repeatable benchmark script
Use a monotonic clock for elapsed durations measured on one machine. It cannot be affected by wall-clock adjustments, so it is appropriate for request duration and local handler timing. For a one-way estimate based on timestamps from two machines, clock synchronization and timestamp quality become part of the measurement. ITU-T Y.1567 discusses the need for accurate time synchronization for one-way delay; a negative calculated offset is a clock or measurement problem, not a delay to convert to a positive value.
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- Define the question and boundary. Decide whether you want request-to-headers time, request-to-complete-body time, connection setup, event age at arrival or receiver processing time. Document whether parsing is inside the timed interval.
- Configure the provider-specific inputs. Get the REST endpoint, WebSocket URL and subscription payload, authentication method, event timestamp field and plan access from the provider’s current documentation. Do not guess these values or hard-code credentials.
- Record the environment. Note runtime and library versions, host and region, connection state, request rate, concurrency, payload size, event volume and workload phase. Pin or document dependencies: the Python example discussed by Orbistats / DEV Community used
httpx,websockets,fastapi,uvicornandpython-dateutil, but its example was not validated here and library APIs can change. - Capture timestamps at the boundary. For REST, start the monotonic timer immediately before sending and stop at the declared response boundary. For WebSocket delivery, record local arrival before expensive parsing and retain the provider’s documented event timestamp. For webhooks, stamp arrival as close as possible to the beginning of request handling, then time handler or acknowledgement work separately if it matters.
- Record failures and exclusions. Include status codes, errors, timeouts, reconnects, retries, missing or unparseable timestamps and valid-sample counts. Do not silently drop failed or invalid observations.
- Repeat under documented load. Run more than once and include idle, representative and peak conditions when they matter. Vary time or load to see how distributions change; a single mean from one run is not a complete performance picture.
Measure REST request duration without confusing it with freshness
For a client-side REST measurement, wrap the request in a monotonic timer and state whether the timer ends when response headers arrive or after the full body has been read. If body reading or JSON parsing is included, say so. Record status, errors and timeouts, and identify whether the connection was warm or newly established; connection reuse changes what the observed duration includes.
This is a round-trip application measurement on one clock. It does not reveal how old the returned data is. If the client polls periodically, detection of a change also includes waiting for the next poll. Under a regular polling pattern, the average wait is half the polling interval; report that polling-related staleness separately from request duration.
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Measure WebSocket setup, messages and event delivery separately
Connection setup
Measure connection establishment on its own. A fast handshake says little about message delivery after the connection is open, so do not combine setup time with steady-state event observations unless you explicitly want a startup metric.
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Ping/Pong round-trip time
Ping/Pong can estimate round-trip time for an established connection; it is not a one-way application event-delivery measurement. The websockets 13.0.1 keepalive and latency documentation describes Ping/Pong timing alongside keepalive, heartbeat and timeout behavior. Its details are version-specific, so verify the API against the library version used. Browser WebSocket APIs do not expose native Ping/Pong, so a browser client that needs comparable heartbeat timing must use an application-level approach.
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Event arrival and inter-arrival gaps
For event age, compare the provider’s documented event-published timestamp with a local arrival timestamp captured before expensive parsing. This is a one-way cross-clock estimate: timestamp semantics, clock alignment and measurement uncertainty all matter. Track the gaps between arrivals as a separate series. A quiet feed can show a low event age while producing few events; irregular or bursty gaps alone do not prove that each message travelled slowly.
Measure webhook delivery, retries and receiver work
A webhook travels from provider to receiver. If you calculate event-to-arrival delay, confirm that the provider supplies a trustworthy event timestamp and that provider and receiver clocks are suitably aligned. Stamp arrival at the start of request handling, then measure parsing, application work or acknowledgement time separately if those are relevant to your question.
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Do not treat an attempt timestamp as interchangeable with an event timestamp. The Standard Webhooks specification distinguishes them: retries can represent a later delivery attempt while retaining the same event identity. Report the provider, attempt number, retry policy and whether retry delay is included. Retry schedules and success criteria depend on the provider; consult its current documentation rather than assuming a general schedule.
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Summarize results so the comparison is useful
For each metric and run, report the number of valid samples, p50, p95 and p99, minimum and maximum, and an explicitly labeled average if it helps. Put errors, timeouts, reconnects, retries, skipped timestamps and other exclusions alongside the distribution so a fast percentile cannot hide missing observations.
Low sample counts are weak evidence for tail percentiles such as p99. Treat repeated runs and varying workload as practical guidance, not as a universal sample-size guarantee. The article by Orbistats / DEV Community recommends reporting distributions and testing at different times; ITU-T Y.1567 likewise emphasizes carefully specified metrics and statistical summaries, particularly under load.
Example result record
metric: REST request, start to complete response body
connection: warm / persistent
workload: request rate, concurrency, payload size
run conditions: host/region, runtime and dependency versions
samples: valid count; errors; timeouts
summary: p50, p95, p99, minimum, maximum, average
excluded: count and reason
Use the same record shape for WebSocket setup, Ping/Pong RTT, event age and inter-arrival gaps, and for webhook event-to-arrival delay and receiver processing. Do not collapse these into one score: they have different boundaries, directions and clock assumptions.
Compare like with like—and state what is not comparable
- Timing boundary: request start to full response, connection setup, message round trip, event publication to arrival, or receiver processing and acknowledgement.
- Direction and clocking: local round trip on one clock versus a one-way estimate across provider and receiver clocks.
- Connection state: cold setup versus an established or persistent connection.
- Load and event pattern: idle, representative and peak load, with request rate, concurrency, payload and event volume stated.
- Distribution and reliability: percentiles, errors, timeouts, reconnects, retries and missing samples.
- Data freshness: request duration versus age of returned data or delivered event.
A REST round trip, WebSocket event age and webhook arrival delay answer different questions; no universal fastest protocol follows from comparing those unlike numbers. If your goal is network-only delay, an application-level HTTP result cannot isolate it from host and stack processing.
Quick Recap
Common interpretation mistakes
- Calling every duration “latency.” Label the measured boundary and direction instead.
- Using wall-clock subtraction for local elapsed time. Use a monotonic timer; reserve cross-host wall-clock comparison for cases with suitable synchronization and stated uncertainty.
- Treating Ping/Pong as event delivery. Keep connection RTT distinct from provider-event-to-arrival timing.
- Ignoring retries or polling. State whether retry delay is counted for webhooks and separate polling wait from REST request duration.
- Reporting only the average. Include sample count, percentiles, failures and exclusions.
- Reading a status page as a benchmark. Status information can help identify a provider incident, but it is not a latency measurement.
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