validating ...\compose.yaml: services.web.healthcheck additional properties 'intervall' not allowed — a key in the Compose file is misspelled or sits at the wrong level. The path before the words names the section, and the quoted word is the key Compose rejected. Correct the spelling or move the key to where it belongs.

Here intervall should be interval. When the path in front is empty, the rejected key is at the top level of the file; in this test it was a service key, environment:, that had lost its indentation.

The error

PS> docker compose -p fix10-cs-p5 config
validating C:\...\p5\compose.yaml: services.web.healthcheck additional properties 'intervall' not allowed

The command exited with code 1. The path to the test folder is shortened; nothing else in the line was changed. The file: 

services:
  web:
    image: alpine
    command: ["echo", "hello"]
    healthcheck:
      test: ["CMD", "true"]
      intervall: 10s

Why it happens

The line starts with validating and the file name: Compose rejected the file itself, and docker compose config printed it without creating a network or a container. healthcheck has no key called intervall, so the key was reported as an extra property of that section. A misspelled key under build gave the same wording with services.web.build as the path: 

validating C:\...\p9\compose.yaml: services.web.build additional properties 'dockerfil' not allowed

An environment: block written at the top level, where it belongs under a service, gave the message with an empty path, which shows as two spaces after the colon: 

services:
  web:
    image: alpine
    command: ["echo", "hello"]
environment:
  TZ: UTC
validating C:\...\p8\compose.yaml:  additional properties 'environment' not allowed

A misspelled key directly under a service printed a different message in the same test, services.web.enviroment false schema; that case has its own post, linked below.

The fix

services:
  web:
    image: alpine
    command: ["echo", "hello"]
    healthcheck:
      test: ["CMD", "true"]
      interval: 10s
PS> docker compose -p fix10-cs-p5 config
name: fix10-cs-p5
services:
  web:
...
    healthcheck:
      test:
        - CMD
        - "true"
      interval: 10s
...

The corrected spelling passed and config printed the resolved file. For the top-level case, indenting environment: under web so that it lines up with image: fixed it, and config printed TZ: UTC under the service. Running docker compose config after every edit catches these before anything starts.

How it was reproduced

Four one-service files checked with docker compose config from Windows PowerShell 5.1: an alpine service with intervall under healthcheck, a service with only a build: block and dockerfil in it, and two alpine services with an environment: block at the top level, and enviroment directly under the service. Docker Compose v5.7.0, Docker Engine 29.9.3, Docker Desktop 4.99.0 on Windows (version 10.0.26300). Nothing was started; the project names with fix10-cs- are this test's own.

Frequently asked

What does 'additional properties not allowed' mean in docker compose?
A key in the file is not one Compose accepts at that place. The path before the words names the section, and the quoted word is the rejected key: a typo or a key at the wrong indentation in the cases tested here.
Why is the path empty in the additional properties error?
The rejected key is at the top level of the file. In this test an environment: block written without indentation, outside the service, gave the message with an empty path.
How do I check a docker-compose.yml for wrong keys?
Run docker compose config. It validates the file without starting anything and printed the additional properties error with exit code 1 for each of the three files tested here.

More decoded errors in the Fixes category. For a misspelled key directly under a service, see Docker Compose: false schema from a misspelled key.