# 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.

## 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

MCP events use these outcome classes:

| 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.                            |

## GraphQL operation types

| Type         | Meaning                                      |
| ------------ | -------------------------------------------- |
| Query        | A read operation.                            |
| Mutation     | A write operation.                           |
| Subscription | A long-lived operation that streams updates. |

## GraphQL error classes

The GraphQL tab groups errors by where they arise:

| Class      | Meaning                                                          |
| ---------- | ---------------------------------------------------------------- |
| Resolver   | A resolver threw while executing the operation.                  |
| Validation | The operation failed schema validation before execution.         |
| Auth       | An authentication or authorization check rejected the operation. |

## Resolver latency (GraphQL)

How long the operation spends executing resolvers, as opposed to **total
latency**, which also covers parsing, validation, and gateway policy time. A
total P95 well above the resolver P95 means the operation spends its time
outside your resolvers.

## Query complexity (GraphQL)

A score for how expensive a GraphQL operation is to execute. The score grows
with the fields and nesting the operation requests. The Operations table reports
the average and maximum complexity per operation. See
[Secure your GraphQL API](../../articles/graphql-security.mdx) for complexity
limits.