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Why does VS Code allow comments in JSON files?
VS Code has separate language modes for JSON and JSON with Comments. JSONC is used for VS Code configuration files such as settings.json, tasks.json and launch.json. In that mode, the editor accepts JavaScript-style line comments (//), block comments (/* ... */) and trailing commas. These extensions are not part of standard JSON.
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The filename alone does not tell you which syntax is active. Check the language-mode indicator in VS Code’s status bar. Select it to change the mode, or configure an extension-to-mode association. Microsoft documents the behavior, but its documentation does not establish when JSONC support began or explain the original design rationale; “for years” and “completely intentional” should not be read as sourced historical claims. Microsoft’s JSON documentation describes the modes and their behavior.
Comments are accepted; trailing commas are warned about
JSONC accepts both line and block comments. It also accepts trailing commas, but Microsoft warns against them and says the editor displays a warning. A file that VS Code can edit in JSONC mode may still fail when another tool reads it as strict JSON.
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What does JSONC look like?
In JSONC mode, VS Code accepts examples like these:
{
// A line comment
"editor.tabSize": 2,
"files.trimTrailingWhitespace": true,
}The comment and the comma after the last property are JSONC conveniences. Remove them if the file must be valid strict JSON. The trailing-comma warning is a useful signal, but the key compatibility question is whether the program that reads the file supports JSONC.
Does schema validation make the file strict JSON?
No. Syntax mode and schema validation answer different questions. The selected language mode determines which syntax VS Code accepts. An associated JSON Schema can separately check whether the document has the expected structure and values, and VS Code can show diagnostics for schema violations. Passing schema checks does not make JSONC syntax acceptable to a strict JSON parser.
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VS Code supports JSON Schema drafts 4 through 7, with limited support for drafts 2019-09 and 2020-12. Validation can be controlled with json.validate.enable. Microsoft documents schema support and validation in its JSON language guide.
How should you associate a schema?
You can associate a schema by adding a $schema property to the document, using the json.schemas setting, or relying on a schema mapping contributed by an extension. The inline property is explicit, but it becomes part of the data. A consumer may reject that extra key if its expected format does not allow it.
When adding a property would change data that another program expects, use a settings-based mapping instead. VS Code documents json.schemas as an alternative to placing $schema in the document. See Microsoft’s guidance on JSON Schema mapping.
Which mode should you use?
- Use JSONC when the file is intended for a VS Code feature or another consumer that supports comments and the other JSONC syntax you use.
- Use strict JSON when a downstream parser expects standard JSON, or when you cannot confirm that it accepts JSONC. Avoid comments and trailing commas in that file.
- Check both syntax and shape when the file must meet a particular data format: select the appropriate language mode and associate a schema for structural and value diagnostics.
For project configuration, VS Code distinguishes user settings from workspace settings. Workspace settings live in the project’s .vscode directory and can be shared with the project; user settings apply to an individual VS Code setup. The settings editor provides IntelliSense for settings.json, and VS Code highlights incorrect setting names and JSON formatting errors. Microsoft’s settings guide explains the scopes.
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What to check when a file works in VS Code but fails elsewhere
- Check the language mode: select the status-bar mode indicator and confirm whether the file is in JSON or JSON with Comments.
- Inspect the syntax: remove comments and trailing commas if the consumer requires strict JSON.
- Identify the consumer’s requirements: editor acceptance does not prove that a separate parser or application accepts the same syntax.
- Separate schema errors from syntax errors: use an associated schema to check expected structure and values, but do not treat schema validation as proof of strict JSON compatibility.
- Review schema placement: if an inline
$schemakey could be rejected as unexpected data, associate the schema throughjson.schemasinstead.
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