---
title: "Get output assertions for a check"
method: GET
path: "/api/v1/checks/{id}/assertions"
tags: ["Checks"]
---

# Get output assertions for a check

`GET /api/v1/checks/{id}/assertions`

## Request

- Base URL: `https://app.lastping.dev`
- URL: `https://app.lastping.dev/api/v1/checks/{id}/assertions`
- Auth: API key in header `X-Api-Key`

Returns the output assertions configured for the check. Returns an
empty `assertions` array when none are set (the overwhelmingly common
case, and the case that must cost at most one indexed lookup on the
ping-processing path).

A ping body that fails any assertion on a `success` signal turns that
signal into a `fail` with cause `assertion` — see the `Assertion`
schema for how each `kind` is evaluated.

## Response `200`

Current output assertions for this check (may be an empty array).

- AssertionsResponse: The complete set of output assertions configured for a check.
  - `assertions` Assertion[], required: Always a JSON array, empty when the check has no assertions configured.
    - `id` string, uuid: Server-assigned. Present on GET/PUT responses; ignored if sent in a PUT request body.
    - `name` string, required: Human label for the assertion. Appears in the alert's failure reason.
    - `kind` 'contains' | 'not_contains' | 'matches' | 'json_path', required: How the body is inspected. `contains`/`not_contains` and `matches` read `value` against the raw body text. `json_path` decodes the body as JSON and compares the value at `path` to `value` using `op`.
    - `value` string: Required for `contains`, `not_contains` and `matches` (substring or RE2 pattern, max 1000 bytes). For `json_path`, the expected value to compare against — compared numerically if both the extracted value and `value` parse as a number (so `"12.5" > "3"` is true), otherwise compared as strings.
    - `path` string: Required for `json_path` only. A dotted path into the body decoded as JSON, e.g. `"result.rows_processed"`. Must not contain `[`, `*` or `$` — this is a fixed lookup, not a query.
    - `op` 'eq' | 'ne' | 'gt' | 'gte' | 'lt' | 'lte': Required for `json_path` only. Comparison operator between the extracted value and `value`.

## Other responses

- `401`: Missing or invalid API key.
- `404`: Check not found in this project.
- `429`: Too many requests. The per-principal fixed-window rate limit has been exceeded. Retry after the number of seconds indicated by the `Retry-After` response header. The problem body's `code` is `RATE_LIMITED`. It names this limiter specifically, so a client can tell it apart from the application-level throttles that also answer 429 with their own codes and their own, much longer, `Retry-After` values (`TEST_PING_RATE_LIMITED`, `TOO_MANY_ATTEMPTS`). Back off globally on `RATE_LIMITED`; back off on the one operation for the others. The principal is the API key for a key-authenticated request and the USER for a browser session, so every tab one person has open shares one budget.

---

[API](https://skmtc.dev/lastping/apis/lastping-management-api.md) · [All operations](https://skmtc.dev/lastping/apis/lastping-management-api/llms.txt) · [OpenAPI document](https://skmtc.dev/lastping/apis/lastping-management-api/revisions/bbc6eda91c46?raw)