Engineering Reliability Metrics Operational

Error Rate

Error Rate: Percentage of requests that result in errors.

Formula

Error Rate = Error responses (5xx) / Total requests × 100

Computable definition

The canonical formula in the GASP formula grammar. The MCP server compiles it to SQL over the datasets listed below.

sum(field.error_count) / sum(field.request_count)

Unit: percent (the formula yields an unscaled ratio)

Notes: Server errors (5xx) divided by total requests.

Data requirements

Grain: Per service per interval, aggregate daily · Frequency: Daily · Aggregation: aggregate (day) · Staged: no · Main source: Monitoring.

Field	Dataset	Type
`error_count`	service_metrics	integer
`period_start`	service_metrics	date
`request_count`	service_metrics	integer

Example SQL (Postgres)

SELECT (CAST((SELECT COALESCE(SUM(error_count), 0) FROM service_metrics WHERE period_start >= :period_start AND period_start <= :period_end) AS DOUBLE PRECISION) / NULLIF((SELECT COALESCE(SUM(request_count), 0) FROM service_metrics WHERE period_start >= :period_start AND period_start <= :period_end), 0)) AS error_rate

From an agent: with the GASP MCP server, call lookup_metric({ "name": "error_rate" }) or generate_query({ "metric": "error_rate", "adapter": "<your adapter JSON>" }).

Benchmarks

Below 0.1%: Excellent
0.1-0.5%: Good
0.5-1%: Acceptable
Above 1%: Needs attention

What It Tells You

Service reliability from user perspective.

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