Conditions DSL

Conditions are simple expressions evaluated after each check. All conditions in a monitor must pass for the check to be considered successful.

Syntax

[VARIABLE] OPERATOR value

• Variable — a bracketed keyword identifying what to check
• Operator — ==, !=, <, >, <=, >=
• Value — a string, number, or boolean

Variables

[STATUS]

HTTP status code as an integer. Only available on HTTP monitors.

conditions:
  - "[STATUS] == 200"
  - "[STATUS] < 400"
  - "[STATUS] != 503"

[RESPONSE_TIME]

Time in milliseconds from sending the request to receiving the response.

Available on both HTTP and TCP monitors.

conditions:
  - "[RESPONSE_TIME] < 500"
  - "[RESPONSE_TIME] < 2000"

[BODY]

Raw response body as a string (HTTP monitors only).

conditions:
  - "[BODY] == ok"

[BODY].path.to.field

JSON dot-path into the response body. UpSlim parses the body as JSON and extracts the value at the given path.

conditions:
  - "[BODY].status == healthy"
  - "[BODY].db.connected == true"
  - "[BODY].version == 1.0.0"

TIP

The response body is only read if at least one condition references [BODY]. This avoids unnecessary memory allocation for large responses.

[CONNECTED]

Whether the TCP connection was established successfully. Only available on TCP monitors.

conditions:
  - "[CONNECTED] == true"

Operators

Operator	Description
==	Equals
!=	Not equals
<	Less than
>	Greater than
<=	Less than or equal
>=	Greater than or equal

Comparison operators (<, >, <=, >=) work on numbers. Equality operators work on strings, numbers, and booleans.

Multiple conditions

All conditions must pass. If any condition fails, the check is marked as failed and the failure reason reports which condition failed.

conditions:
  - "[STATUS] == 200"         # must pass
  - "[RESPONSE_TIME] < 500"  # must pass
  - "[BODY].ok == true"       # must pass

Failure log example:

WARN  Check FAILED monitor=api response_time_ms=612 reason=Some("[RESPONSE_TIME] < 500: got '612'")

Examples

HTTP health endpoint returning JSON

- name: api
  type: http
  url: "https://api.example.com/health"
  conditions:
    - "[STATUS] == 200"
    - "[RESPONSE_TIME] < 1000"
    - "[BODY].status == healthy"

HTTP with auth header

- name: internal-api
  type: http
  url: "https://internal.example.com/status"
  headers:
    Authorization: "Bearer ${API_TOKEN}"
  conditions:
    - "[STATUS] == 200"
    - "[BODY].ready == true"

TCP database check

- name: postgres
  type: tcp
  host: "db.internal"
  port: 5432
  timeout: 3s
  conditions:
    - "[CONNECTED] == true"
    - "[RESPONSE_TIME] < 100"