How do I open a floating window showing diagnostic details at the cursor using a built-in Neovim key?

Explanation

Neovim 0.10+ includes <C-w>d as a built-in normal-mode key that opens a floating window displaying the full diagnostic message at the cursor position. No configuration or plugins are required — it works out of the box wherever LSP or diagnostic providers are active.

How it works

• <C-w>d is bound by default to vim.diagnostic.open_float() in Neovim 0.10+
• The float shows the full diagnostic text, severity, and source (e.g. which LSP reported the error)
• Press <C-w>d again (or any key) to close the float
• Unlike virtual text which truncates long messages, the float always shows the complete diagnostic

Example

With the cursor on a line that has an LSP error:

Press <C-w>d

A floating window appears:

┌─────────────────────────────────────────────┐
│ E: cannot find value `foo` in this scope    │
│ rust-analyzer                               │
└─────────────────────────────────────────────┘

Tips

• If multiple diagnostics are on the same line, the float shows them all
• To navigate between diagnostics, use ]d / [d (Neovim 0.10+ defaults)
• To customize the float appearance, configure vim.diagnostic.config({float = {...}})
• This works for any diagnostic source: LSP, null-ls, linters, etc.