Metrics Glossary
This page defines every term used in the Analytics dashboards once. KPI tables on tab pages link here for depth.
HTTP status classes
| Class | Meaning |
|---|---|
| 2xx | Success. |
| 3xx | Redirection. |
| 4xx | Client error. The caller sent something the gateway or backend rejected. |
| 5xx | Server error. The gateway, an upstream origin, or an MCP backend failed to fulfill the request. |
Error rates
Client error rate. 4xx count divided by total requests in the window, expressed as a percentage.
Server error rate. 5xx count divided by total requests in the window.
Request-weighted average. When aggregating a rate across many entities (consumers, agents, origins), each entity's rate is weighted by its request count. A consumer with 100,000 requests at a 1% error rate contributes more than a consumer with 100 requests at a 50% error rate. Use the request-weighted figure to answer "what does the average request experience look like?"; use a simple unweighted average to answer "what does the average consumer experience look like?"
Latency
Avg latency. Arithmetic mean response time. Sensitive to outliers.
P50 (median) latency. Half of requests completed within this time.
P95 latency. 95% of requests completed within this time. The other 5% took longer. P95 is the standard tail-latency metric.
P99 latency. 99% of requests completed within this time. Useful for spotting outlier behavior that P95 may smooth over.
Latency distribution histogram. Bands at P10, P50, P90, P95, P99. Clicking a band on the Requests tab filters to requests in that duration range.
Active edge instances
Distinct gateway worker instances actively serving traffic in each interval. A rough indicator of how widely your traffic is distributed.
Active sessions (MCP Server)
Distinct MCP sessions, estimated using HyperLogLog. The figure is approximate but monotonic within a single time window. Accurate enough for trend analysis, not for exact session counting.
Failure origin
Classifies an error by where it originated:
| Origin | Meaning |
|---|---|
| gateway | The Zuplo gateway returned the error. |
| upstream | A backend origin or MCP server returned the error. |
| client | The client sent something invalid that caused the failure. |
Outcome class
Used on MCP Gateway events:
| Class | Meaning |
|---|---|
| success | Event completed normally. |
| application_error | Event failed due to an application-layer issue (e.g. invalid input). |
| gateway_error | The gateway itself returned an error. |
| upstream_error | An upstream MCP server returned an error. |
Tokens (AI Gateway)
| Type | Meaning |
|---|---|
| Prompt | Tokens in the request the gateway forwarded to the model. |
| Completion | Tokens in the model's response. |
| Embedding | Tokens consumed by embedding requests. |
Estimated cost (AI Gateway)
Computed from token usage × the model's published pricing. Does not include discounts, credits, or provider-side rounding. Use it for trend analysis, not invoice reconciliation.