Service Level Indicator

observability.calculate_sli

ProductionBounded custom (Class B)Deterministicstrictfastv1.0.0

No network

Overview

You send the events, the window and a closed set of good-event predicates, and we return the indicator as a ratio in zero to one, the counts behind it, and the sub-windows that fell below your objective. Every event is good, bad or invalid, and invalid events leave the denominator and are reported, because an availability figure over a denominator that silently shrank is worse than no figure. An empty window is a verdict rather than a failure, so this can be called on a schedule at three in the morning. The window is yours: we read no clock and fetch nothing.

Writing this by hand is where availability numbers go wrong: the denominator quietly drops unparseable events, the boundary is inclusive at both ends so adjacent hours double-count, and the breach test compares an unrounded value against a rounded one.

Reliability

Fully deterministic and clock-free: the same events and window always give the same value, and nothing about the answer depends on when you asked. Rounding is half-up at your scale and the breach comparison uses the rounded value. Failures, none worth retrying unchanged: OBS_SLI_INPUT_MISSING means events or buckets was absent or empty for the kind you chose, so send the one that kind consumes. OBS_SLI_INPUT_AMBIGUOUS means both events and buckets arrived, so send one. OBS_SLI_INPUT_TOO_LARGE means the events or buckets array went past the 2097152-byte inline ceiling, so send fewer entries or fewer fields each. OBS_SLI_WINDOW_INVALID means end was not after start, the span fell outside 1 millisecond to 366 days, or the window object was missing. OBS_SLI_TIMESTAMP_INVALID means a timestamp was absent, unparseable or carried no offset, and the answer names its position. OBS_SLI_OFFSET_MIXED means the list mixed offsets under REQUIRE_UNIFORM or carried a non-UTC one under REQUIRE_UTC, and both positions are named. OBS_SLI_KIND_UNSUPPORTED means the kind is not one of the four. OBS_SLI_PREDICATE_UNSUPPORTED means a predicate type or a status class is not in the vocabulary. OBS_SLI_PREDICATE_INVALID means a predicate had the wrong shape, an empty value list or a threshold out of range. OBS_SLI_SPEC_FIELD_MISSING means kind, goodWhen, latencyField or thresholdMs was required for your kind and absent. OBS_SLI_OBJECTIVE_INVALID means the objective fell outside 0.5 to 0.999999 or carried more than 6 decimal places. OBS_SLI_BUCKET_INVALID means bucketDurationSeconds was missing, out of range or sent without an objective, or a bucket's good exceeded its total. OBS_SLI_BUCKET_LIMIT_EXCEEDED means the window divides into more than 10000 buckets, or more than 10000 counters arrived, so widen the bucket. OBS_SLI_EVENT_LIMIT_EXCEEDED means more than 50000 events arrived, so split the window and combine the counts yourself. OBS_SLI_SAMPLE_NON_FINITE means a latency field carried an infinity or a not-a-number, which is a producer defect rather than an invalid event. OBS_SLI_OPTION_UNSUPPORTED means a property, a scale or an offset policy is not one we accept. OBS_SLI_WORK_REFUSED means the projected work went past 410000 units, where a latency threshold counts as one predicate, and the answer carries the projection and the budget.

Context footprint

Echoes no event; the answer is a value, seven counts and at most 1000 breach entries, so it stays small whatever you send. A successful call costs 2 execution credits.

When to use it

When you hold the events or the counters and want a defensible ratio, its counts, and the sub-windows that breached.

When you want a burn rate against an error budget, a percentile of a latency series, or a deadline on a working calendar.

Scope

Note

Compute one ratio-valued service level indicator over one caller-declared window, and list the sub-windows that fell below the objective.

Non-goals

Does not fetch, scrape or store any metric or event
Does not read a clock — every window boundary arrives in the request
Does not evaluate a boolean expression language, only allOf over a closed set
Does not compute a deadline against a working calendar
Does not report a percentage; every value is a ratio between 0 and 1

Properties

IdempotentRetry safeStreaming supportedFile input supportedRequires external service

Capabilities

analysis

Cost & billing

Flat rate per invocation

MetercallsBillable onsuccessCost per call2 credits

File handling

Accepts file_refProduces file_refMax input2 MB

How we handle your data

Sensitive input, safe output

What this means

This skill may receive sensitive content, but it does not target sensitive data and returns only a structured non-sensitive result.

Squillify guarantees

Runs inside Squillify
This skill runs inside Squillify.
Payloads are not sent to an external service by this skill.
Squillify does not permanently store submitted payloads.
Telemetry records metadata only, not submitted content.
Submitted payloads are not used for training.
Submitted payloads are not reviewed by humans.
This skill does not target sensitive data.
The response does not contain submitted content.

Your responsibility

Squillify does not determine whether submitted content is sensitive. Your application is responsible for deciding what data it is allowed to submit. Your application is responsible for securing the response.

Read the Microskill Data Handling Policy

Input schema

Field	Type	Required	Description
events	array	No	Required unless buckets is provided. 1 to 50000 events each carrying t plus predicate fields.
buckets	array	No	Required unless events is provided. 1 to 10000 {t, good, total} counters for AGGREGATE_RATIO.
window	object	Yes	Closed half-open window [start, end) as ISO-8601 instants with explicit offsets.
sliSpec	object	Yes	Closed indicator spec: kind, 1 to 8 goodWhen predicates, and latencyField plus thresholdMs only for LATENCY_THRESHOLD_COMPLIANCE.
objective	number	No	Ratio between 0.5 and 0.999999; omit it for the indicator with no verdict and an empty breaches list.
bucketDurationSeconds	integer	No	Required unless objective is omitted. Bucket width from 1 through 86400 seconds.
scale	integer	No	Decimal places from 0 through 12; omit it for 6.
offsetPolicy	string	No	Offset mixing rule; omit it for REQUIRE_UNIFORM.

Output schema

Field	Type	Required	Description
value	number	Yes	Indicator as a ratio between 0 and 1 at your scale, or JSON null when the window held no valid event.
verdict	string	Yes	MET, BREACHED, UNDEFINED_EMPTY_WINDOW, UNDEFINED_NO_VALID_EVENTS, or JSON null when you supplied no objective.
window	object	Yes	Parsed window as we applied it, with the inclusivity literal and durationSeconds added so a stored verdict names the interval it judged.
counts	object	Yes	Closed counters: examined, inWindow, outOfWindow, good, bad, valid and invalid.
invalidRatio	number	Yes	Invalid events over in-window events at your scale, or JSON null for an empty window.
breaches	array	Yes	Up to 1000 sub-windows below the objective, each {bucketStart, bucketEnd, value, validCount, shortfall}; empty without an objective.
summary	object	Yes	Closed publication receipt with kind, optional objective, bucketDurationSeconds, bucketCount, breachCount, breachesTruncated, undefinedBucketCount, scale and roundingMode.

API contract

POST /v1/execute

curl

curl -sS -X POST "$BASE/v1/execute" -H "Authorization: Bearer $KEY" -H 'Content-Type: application/json' -d '{"skillKey":"observability.calculate_sli","input":{"events":[{"t":"2026-07-29T10:00:00Z","status":200}],"window":{"start":"2026-07-29T10:00:00Z","end":"2026-07-29T11:00:00Z"},"sliSpec":{"kind":"AVAILABILITY_RATIO","goodWhen":[{"type":"statusCodeIn","field":"status","values":[200]}]}}}'

Integrations

TypeScript SDK

import { Squillify } from "@squillify/sdk";

const sq = new Squillify({ apiKey: process.env.SQUILLIFY_API_KEY });

const { output } = await sq.execute("observability.calculate_sli", {"events":[{"status":200,"t":"2026-07-29T10:00:00Z"},{"status":200,"t":"2026-07-29T10:15:00Z"},{"status":503,"t":"2026-07-29T10:30:00Z"},{"status":200,"t":"2026-07-29T11:00:00Z"}],"objective":0.99,"window":{"start":"2026-07-29T10:00:00Z","end":"2026-07-29T11:00:00Z"},"sliSpec":{"goodWhen":[{"type":"statusCodeClassIn","field":"status","classes":["S2XX","S3XX"]}],"kind":"AVAILABILITY_RATIO"},"bucketDurationSeconds":1800});

Errors

Code	HTTP	Retryable	Description
VALIDATION_ERROR	400	No	The request payload failed schema validation.
UNAUTHORIZED	401	No	Missing or invalid API key.
SKILL_NOT_ACCESSIBLE	403	No	The API key is not granted access to this skill.
SKILL_NOT_AVAILABLE_FOR_PLAN	403	No	This skill is not included in your current plan.
PLAN_ELIGIBILITY_UNAVAILABLE	503	Yes	Plan eligibility could not be decided. Retry after backoff.
SKILL_NOT_FOUND	404	No	The requested skill or version does not exist.
TENANT_RATE_LIMITED	429	Yes	Request rate limit exceeded. Retry after backoff.
QUOTA_EXCEEDED	429	Yes	Plan quota exhausted. Retryable once the quota period resets.
EXECUTION_TIMEOUT	504	Yes	Execution exceeded the allowed time budget.
OBS_SLI_INPUT_MISSING	400	No	The request payload failed this skill's input validation.
OBS_SLI_INPUT_AMBIGUOUS	400	No	The request payload failed this skill's input validation.
OBS_SLI_INPUT_TOO_LARGE	429	No	A size, quota, rate, or time limit was exceeded.
OBS_SLI_WINDOW_INVALID	400	No	The request payload failed this skill's input validation.
OBS_SLI_TIMESTAMP_INVALID	400	No	The request payload failed this skill's input validation.
OBS_SLI_OFFSET_MIXED	400	No	The request payload failed this skill's input validation.
OBS_SLI_KIND_UNSUPPORTED	400	No	The skill does not support the requested variant.
OBS_SLI_PREDICATE_UNSUPPORTED	400	No	The skill does not support the requested variant.
OBS_SLI_PREDICATE_INVALID	400	No	The request payload failed this skill's input validation.
OBS_SLI_SPEC_FIELD_MISSING	400	No	The request payload failed this skill's input validation.
OBS_SLI_OBJECTIVE_INVALID	400	No	The request payload failed this skill's input validation.
OBS_SLI_BUCKET_INVALID	400	No	The request payload failed this skill's input validation.
OBS_SLI_BUCKET_LIMIT_EXCEEDED	429	No	A size, quota, rate, or time limit was exceeded.
OBS_SLI_EVENT_LIMIT_EXCEEDED	429	No	A size, quota, rate, or time limit was exceeded.
OBS_SLI_SAMPLE_NON_FINITE	400	No	The request payload failed this skill's input validation.
OBS_SLI_OPTION_UNSUPPORTED	400	No	The skill does not support the requested variant.
OBS_SLI_WORK_REFUSED	429	No	A size, quota, rate, or time limit was exceeded.

Other limits

Limit	Value
Recommended inline bytes	32 KiB

Limitations

Does not fetch, scrape or store any metric or event
Does not read a clock — every window boundary arrives in the request
Does not evaluate a boolean expression language, only allOf over a closed set
Does not compute a deadline against a working calendar
Does not report a percentage; every value is a ratio between 0 and 1
Computing when a support agreement's clock runs out, which business.sla_deadline answers
Comparing an observed value against a burn-rate alert, which observability.evaluate_slo_burn answers

How to call

POST /v1/execute (requires authentication)

Request bodyjson

{
  "skillKey": "observability.calculate_sli",
  "input": {
    "events": [
      {
        "status": 200,
        "t": "2026-07-29T10:00:00Z"
      },
      {
        "status": 200,
        "t": "2026-07-29T10:15:00Z"
      },
      {
        "status": 503,
        "t": "2026-07-29T10:30:00Z"
      },
      {
        "status": 200,
        "t": "2026-07-29T11:00:00Z"
      }
    ],
    "objective": 0.99,
    "window": {
      "start": "2026-07-29T10:00:00Z",
      "end": "2026-07-29T11:00:00Z"
    },
    "sliSpec": {
      "goodWhen": [
        {
          "type": "statusCodeClassIn",
          "field": "status",
          "classes": [
            "S2XX",
            "S3XX"
          ]
        }
      ],
      "kind": "AVAILABILITY_RATIO"
    },
    "bucketDurationSeconds": 1800
  }
}

Examples

Availability over four events, one of them out of the window

Inputjson

{
  "events": [
    {
      "status": 200,
      "t": "2026-07-29T10:00:00Z"
    },
    {
      "status": 200,
      "t": "2026-07-29T10:15:00Z"
    },
    {
      "status": 503,
      "t": "2026-07-29T10:30:00Z"
    },
    {
      "status": 200,
      "t": "2026-07-29T11:00:00Z"
    }
  ],
  "objective": 0.99,
  "window": {
    "start": "2026-07-29T10:00:00Z",
    "end": "2026-07-29T11:00:00Z"
  },
  "sliSpec": {
    "goodWhen": [
      {
        "type": "statusCodeClassIn",
        "field": "status",
        "classes": [
          "S2XX",
          "S3XX"
        ]
      }
    ],
    "kind": "AVAILABILITY_RATIO"
  },
  "bucketDurationSeconds": 1800
}

Expected outputjson

{
  "value": 0.666667,
  "invalidRatio": 0,
  "counts": {
    "examined": 4,
    "inWindow": 3,
    "outOfWindow": 1,
    "good": 2,
    "bad": 1,
    "valid": 3,
    "invalid": 0
  },
  "verdict": "BREACHED",
  "breaches": [
    {
      "bucketStart": "2026-07-29T10:30:00Z",
      "bucketEnd": "2026-07-29T11:00:00Z",
      "value": 0,
      "validCount": 1,
      "shortfall": 0.99
    }
  ],
  "summary": {
    "kind": "AVAILABILITY_RATIO",
    "objective": 0.99,
    "bucketDurationSeconds": 1800,
    "bucketCount": 2,
    "breachCount": 1,
    "breachesTruncated": false,
    "undefinedBucketCount": 0,
    "scale": 6,
    "roundingMode": "HALF_UP"
  },
  "window": {
    "start": "2026-07-29T10:00:00Z",
    "end": "2026-07-29T11:00:00Z",
    "inclusivity": "[start,end)",
    "durationSeconds": 3600
  }
}

Tip

The event exactly on the window end is excluded by the half-open rule, so two of three in-window events are good and the second half-hour is reported as the bucket that breached.

Latency compliance against a threshold, with the breaching half-hour