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Fix "mapping values are not allowed here" in YAML configs

Solve YAML indentation and syntax errors causing the mapping values are not allowed here exception.

The Problem (Error Root Cause)Exception

Your CI/CD pipeline or Docker Compose is failing with `mapping values are not allowed here`. This usually means a colon `:` is missing a space after it, or your indentation is incorrect.

Identified via runtime validation & stack traces

The Solution (Step-by-Step Fix)Verified

YAML is strictly whitespace dependent. Ensure that every key-value pair has a space after the colon, and that block sequences use consistent spaces (not tabs). Converting your YAML to JSON can highlight structural flaws.

Deterministic, non-destructive resolution

Code Standard: Bad Pattern vs Verified Fix

Live Syntax

Anti-Pattern vs Verified Fix

1// ❌ Bad: Missing space after colon
2services:
3  web:
4    image:nginx
5    ports:
6      - 80:80
7 
8// ✅ Good: Correct spacing and indentation
9services:
10  web:
11    image: nginx
12    ports:
13      - "80:80"

Test and resolve this using YAML to JSON / JSON to YAML Converter

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Frequently Asked Questions

Q:Can I use tabs in YAML?

No, the YAML specification forbids tabs for indentation. Always use spaces.

Q:How do I debug complex YAML?

Convert it to JSON using our YAML to JSON converter. JSON is stricter and tooling will immediately flag structural issues.

Related Troubleshooting Guides

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yaml

Fix "did not find expected key while parsing a block mapping"

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