YAML — LSP setup

• Builtin server: yaml-ls — yaml-language-server --stdio
• Extensions: .yaml .yml
• Install hint: npm install -g yaml-language-server

Install

• macOS: npm install -g yaml-language-server
• Linux: npm install -g yaml-language-server
• Windows: npm install -g yaml-language-server (PowerShell)

Confirm it resolves:

command -v yaml-language-server

Configure

Builtin — usually NO config needed (auto-resolved by extension). Configure only to set priority, init options, override extensions, or disable. Same JSON shape in .codex/lsp-client.json (Codex) AND .opencode/lsp.json (OpenCode/omo):

{ "lsp": { "yaml-ls": { "priority": 100 } } }

For builtin ids in a PROJECT config, command is supplied automatically — only set priority/initialization/extensions/disabled/env. A fully custom (non-builtin) server with its own command must go in the USER config (~/.codex/lsp-client.json).

Initialization options (only if commonly needed)

Schema association is the main reason to configure yaml-ls. Map globs to a schema URL or local path under yaml.schemas:

{
  "lsp": {
    "yaml-ls": {
      "initialization": {
        "yaml": {
          "schemas": {
            "https://json.schemastore.org/github-workflow.json": ".github/workflows/*.yml",
            "https://json.schemastore.org/kustomization.json": "kustomization.yaml",
            "./schemas/my-config.schema.json": "config/*.yaml"
          },
          "validate": true,
          "completion": true,
          "format": { "enable": true }
        }
      }
    }
  }
}

Set "yaml.schemaStore": { "enable": true } to auto-resolve schemas from SchemaStore (catalog at https://www.schemastore.org/). Inline # yaml-language-server: $schema=<url> modelines also work without config.

Alternatives

• redhat.vscode-yaml bundles the same server in editors.
• yamllint standalone for style/lint-only checks.

Troubleshooting

• PATH: yaml-language-server on PATH; reopen shell after npm -g install.
• No validation: no schema matched — add a yaml.schemas glob or a $schema modeline.
• Wrong schema applied: SchemaStore guessed by filename; pin explicitly under yaml.schemas.

Verify

bun ../../scripts/verify-lsp.ts path/to/file.yaml