PowerShell Diagnostics (PSES)

PowerShell diagnostics for Claude Code

As Claude edits a .ps1, .psm1, or .psd1, this plugin runs real PowerShell Editor Services + PSScriptAnalyzer over that file and feeds the result -- syntax errors and lint findings, with fix suggestions -- straight back into Claude's context, so a mistake gets caught and corrected in the same turn. It is language tooling, not project tooling: near-zero always-on token cost, a language server spawns only when a PowerShell file is open, and one warm process serves the whole session, so each edit pays a fast pipe round-trip instead of a cold start.

See it catch something. Ask Claude to write:

function Frobnicate-Thing { Get-Process }

and the PostToolUse hook returns, right in Claude's context:

The cmdlet 'Frobnicate-Thing' uses an unapproved verb. (PSUseApprovedVerbs)

Claude sees its own mistake and corrects it without you switching tools.

Install in under a minute. Requires pwsh (PowerShell 7+) on your PATH; then, in Claude Code:

/plugin marketplace add manderse21/claude-powershell-lsp
/plugin install powershell-lsp@claude-powershell-lsp
/plugin enable powershell-lsp

Start a new session and you are running. The full prerequisites, the self-bootstrap sequence, and the preflight doctor are in Quick start below.

What works today. The per-file diagnostic loop above is live on every supported host right now. Hover, go-to-definition, and find-references now also serve to Claude Code's native LSP client through an opt-in handshake shim (nativeServe = shim) that works around the upstream Claude Code client init-handshake bug locally; it is off by default while that upstream fix is pending, and workspace-wide analysis remains on the roadmap. Details: Native serve and Why a hook, not native registration.

Prerequisites

Check these before you start; the Quick start below runs them in order.

• PowerShell 7+ (pwsh) on your PATH. As of 1.1.1 the plugin's hooks launch under pwsh; Windows PowerShell 5.1 alone cannot bootstrap them. Check with pwsh -v; if it is missing, step 1 of the Quick start installs it.
• Internet access on the first enabled session. PowerShell Editor Services (PSES) and PSScriptAnalyzer are downloaded on first use, not vendored (see Pinned versions for the exact pins). The download is idempotent and marker-gated -- it runs once and no-ops every session after. Offline or behind a proxy, the first run surfaces an honest unavailable banner instead of failing silently (see Diagnostics status).
• On managed / locked-down Windows, a security control (WDAC / AppLocker / ExecutionPolicy / Constrained Language Mode) can block a downloaded component; it then reads as unavailable rather than crashing. See Troubleshooting.

Windows PowerShell 5.1 can still serve as the PSES child host (set ps_host to powershell); it simply cannot launch the hooks themselves. See Platform support.

Quick start

Copy-paste, top to bottom:

# 1. Prerequisite (run in a terminal) -- skip if `pwsh -v` already works:
winget install Microsoft.PowerShell

# 2. In Claude Code -- add the marketplace, install, then enable the plugin:
/plugin marketplace add manderse21/claude-powershell-lsp
/plugin install powershell-lsp@claude-powershell-lsp
/plugin enable powershell-lsp

# 3. Start a new session (or run /reload-plugins) so the hooks load and the first
#    SessionStart bootstraps PSES + the warm daemon.