Claude Code / AI Coding Tools

Claude Code Bash tool and SessionStart hooks fail with EEXIST on Windows due to non-idempotent mkdir

Fix Claude Code Bash tool crashing on Windows with EEXIST error when session-env directory already exists Includes evidence for Claude Code troubleshooting demand.

Source-backed Last updated May 16, 2026 1 source Needs local verification

Category: AI Coding Tools
Error signature: EEXIST: non-idempotent mkdir of session-env
Quick fix: Compare the failing environment with a known working setup, then change one configuration value at a time.
Updated: May 16, 2026
Verification status: Source-backed
Evidence: 1 public source URL

Before you change production

This page includes public source URLs in the imported troubleshooting record. Compare those references with your version and environment before applying changes.

Reproduce the smallest failing action and save non-secret logs before changing configuration.
Check versions for Claude Code, related SDKs, package managers, CI runners, and hosting providers.
Change one setting or dependency at a time, then rerun the same failing command or request.
Avoid destructive commands, credential rotation, billing changes, or security relaxations without a rollback plan.

What this error means

EEXIST: non-idempotent mkdir of session-env is a Claude Code failure pattern reported for developers trying to fix claude code bash tool crashing on windows with eexist error when session-env directory already exists. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

GitHub issue #59622 filed 2026-05-16 against anthropics/claude-code repo, labeled bug+platform:windows+area:bash+area:hooks. Non-idempotent mkdir causes EEXIST on every SessionStart. Category mapped to AI Coding Tools per Claude Code -> AI Coding Tools rule.

Common causes

GitHub issue #59622 filed 2026-05-16 against anthropics/claude-code repo, labeled bug+platform:windows+area:bash+area:hooks. Non-idempotent mkdir causes EEXIST on every SessionStart. Category mapped to AI Coding Tools per Claude Code -> AI Coding Tools rule.

Quick fixes

Confirm the exact error signature matches EEXIST: non-idempotent mkdir of session-env.
Check the Claude Code account, local tool state, and provider configuration involved in the failing workflow.
Compare the failing environment with a known working setup, then change one configuration value at a time.

Platform/tool-specific checks

Verify the command, editor, extension, or API client that produced the error.
Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
Avoid deleting credentials, local model data, or project settings until the failing scope is clear.

Step-by-step troubleshooting

Capture the exact error message and the command, editor action, or request that triggered it.
Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
Review the source evidence below and compare it with your environment.
Apply one change at a time and rerun the smallest failing action.
Keep the working fix documented for the team or deployment environment.

How to prevent it

Keep provider/tool configuration documented.
Record non-secret diagnostics such as tool version, provider name, model name, and command path.
Add a lightweight check before CI or production workflows depend on the tool.

Diagnostic flow for this page

Match EEXIST: non-idempotent mkdir of session-env exactly before applying the quick fix.
Compare the failing environment with Claude Code versions, account scope, provider settings, and deployment context.
Check the listed common causes in order, starting with the cause that best matches your logs.
Use the evidence status below to decide whether to confirm against public sources or official documentation.
Apply one reversible change, rerun the smallest failing action, and keep rollback notes.

FAQ

What does EEXIST: non-idempotent mkdir of session-env mean in Claude Code?

EEXIST: non-idempotent mkdir of session-env indicates the workflow described by "Claude Code Bash tool and SessionStart hooks fail with EEXIST on Windows due to non-idempotent mkdir" failed in a AI Coding Tools context. Start by confirming the exact signature and the component that emitted it.

What should I check first for EEXIST: non-idempotent mkdir of session-env?

Check whether this cause matches your environment: GitHub issue #59622 filed 2026-05-16 against anthropics/claude-code repo, labeled bug+platform:windows+area:bash+area:hooks. Non-idempotent mkdir causes EEXIST on every SessionStart. Category mapped to AI Coding Tools per Claude Code -> AI Coding Tools rule.

Is the EEXIST: non-idempotent mkdir of session-env guidance source-backed?

The "Claude Code Bash tool and SessionStart hooks fail with EEXIST on Windows due to non-idempotent mkdir" page is labeled source-backed. It has 1 public source URL from github.com, so use that evidence status when deciding how much additional verification you need.

When should I avoid the quick fix for EEXIST: non-idempotent mkdir of session-env?

For "Claude Code Bash tool and SessionStart hooks fail with EEXIST on Windows due to non-idempotent mkdir", avoid applying "Compare the failing environment with a known working setup, then change one configuration value at a time." when the error text differs, the affected version or provider is different, or the change would touch credentials, billing, DNS, production deploy settings, or irreversible data.

What should I collect before debugging EEXIST: non-idempotent mkdir of session-env?

For "Claude Code Bash tool and SessionStart hooks fail with EEXIST on Windows due to non-idempotent mkdir", collect the failing Claude Code command or request, non-secret configuration, versions, timestamps, request IDs when available, and the smallest reproduction that still triggers the signature.