custom-metrics
Emit and query Vercel Custom Metrics. Use when instrumenting application or business measurements in Vercel Functions, using metric() from @vercel/functions, choosing metric names and attributes, or querying emitted values with vc metrics.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/vercel/vercel-plugin --skill custom-metrics- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads custom-metrics automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
Vercel Custom Metrics
Use Custom Metrics for numeric application and business measurements emitted by server-side code running in a Vercel Function. The workflow is emit a numeric sample with metric() → invoke the deployed function → discover and query the metric with vc metrics or Observability.
Emit a metric
Install or upgrade @vercel/functions, then import metric from its root entry point:
pnpm add @vercel/functions
import { metric } from '@vercel/functions';
export async function POST() {
const startedAt = performance.now();
try {
await createOrder();
metric('orders.created', 1, { outcome: 'success' });
return Response.json({ ok: true });
} catch (error) {
metric('orders.created', 1, { outcome: 'error' });
throw error;
} finally {
metric('orders.duration_ms', performance.now() - startedAt);
}
}
The signature is:
metric(name: string, value: number, tags?: Record<string, string>): void
nameidentifies one stable measurement, such asorders.createdororders.duration_ms.valueis the numeric sample. Emit1for an increment that will be summed; emit the observed value for a duration, size, or score.tagsare optional string attributes. After ingestion, discovered tag keys appear as dimensions for filtering and grouping.metric()is synchronous and returnsvoid; do notawaitit.- The helper is a no-op when the runtime does not expose Custom Metrics support. Verify instrumentation through a deployed Vercel Function invocation, not local execution alone.
Model metrics for useful queries
- Prefer stable, dotted names with a unit suffix where useful:
checkout.completed,checkout.duration_ms,queue.batch_size. - Do not use the reserved
vercel.prefix for application-defined names. - Keep variable data in tags instead of metric names. Use
checkout.completedwith{ plan: 'pro' }, notcheckout.completed.pro. - Keep tag cardinality bounded. Good tags are
outcome,plan,provider, or a normalized route. Do not attach user IDs, request IDs, email addresses, raw URLs, or other unique or sensitive values. - Emit one sample at the point where the outcome is known. For retryable or at-least-once work, decide whether attempts or successful logical operations are the intended measurement and name the metric accordingly.
Choose the query aggregation to match what was emitted:
| Measurement | Emit | Query |
|---|---|---|
| Occurrence or increment | metric('checkout.completed', 1) | sum or persecond |
| Duration or size | metric('checkout.duration_ms', duration) | avg, p75, p95, max |
| Sampled level | metric('queue.batch_size', size) | avg, min, max, percentiles |
Discover and query the metric
Run the deployed code at least once, then use the linked project and correct team scope:
vc metrics schema
vc metrics schema orders.duration_ms
vc metrics orders.created -a sum --group-by outcome --since 24h
vc metrics orders.duration_ms -a p95 --since 1h
vc metrics orders.duration_ms -a p95 --group-by outcome --since 24h --format=json
vc and vercel are equivalent. Always inspect the exact metric first with vc metrics schema <name> because the schema reports the available aggregations and discovered tag dimensions. Use -S <team> and -p <project> when the current link or scope is ambiguous; use --all only for a deliberate team-wide query.
Custom Metrics querying requires Observability Plus and availability for the selected team. If a metric is missing:
- Confirm the function was deployed to Vercel and the instrumented path actually ran.
- Confirm
@vercel/functionsexportsmetric; upgrade it if necessary. - Check
vc whoami, the selected team, and the linked project. - Allow for ingestion delay, then rerun
vc metrics schema. - Confirm Observability Plus and Custom Metrics are enabled for the team.
Use the right signal
- Use Custom Metrics for numeric values you want to aggregate, trend, and filter.
- Use Web Analytics custom events for user interaction and conversion events in Web Analytics.
- Use OpenTelemetry spans for traces, operation timing, and request causality.
- Use logs for detailed diagnostic context and individual records.
Do not encode detailed event payloads into metric tags. Pair a low-cardinality metric with structured logs or traces when investigation needs per-request detail.
FAQ
What does the custom-metrics skill do?
Emit and query Vercel Custom Metrics. Use when instrumenting application or business measurements in Vercel Functions, using metric() from @vercel/functions, choosing metric names and attributes, or querying emitted values with vc metrics.
How do I install custom-metrics?
Run npx skills add https://github.com/vercel/vercel-plugin --skill custom-metrics in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/custom-metrics/ (personal) or .claude/skills/custom-metrics/ (project).
Which AI agents can use custom-metrics?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is custom-metrics safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains custom-metrics?
It is published by vercel in vercel/vercel-plugin. It has 102 recorded installs.
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