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CLR Activation Debugging · dotnet | DecimalAI

codingby dotnet

CLR Activation Debugging

dotnet/clr-activation-debugging

Source dotnet/skills ↗License MIT

Diagnoses .NET Framework CLR activation issues using CLR activation logs (CLRLoad logs) produced by mscoree.dll.

SkillScore82Maintained

Automatic

Coding pack

Last verified 9/9/2026

What it changes

Passed 14 of 17 test cases with the skill, and 9 of 17 without it.

Without skill55%

With skill82%

Checks it passed that the model alone missed

Identifies COMPLUS_CLRLoadLogDir as the environment variable.
Identifies 0x80131704 as CLR_E_SHIM_LEGACYRUNTIMEALREADYBOUND.
Identifies ImplementedInThisVersion as the registry subkey under the version key.

and 7 more in the full report

7 fixed11 passed either way3 still failing1 broke

Pass-rate lift: +27 pp
Tokens: +171%
Agent turns: 0%
Response time: -31%

Model gemini-3.6-flashMeasured 9/9/2026v218 of 22 cases passed with skill · 17 comparable

Tokens, turns and time describe resource use, not a dollar price.

Use this skill

Save it into your project's skills folder. Claude Code picks it up in its next session.

curl -fsSL --create-dirs -o .claude/skills/dotnet-clr-activation-debugging/SKILL.md https://app.decimal.ai/s/dotnet-clr-activation-debugging/SKILL.md

Want it pinned and updatable? pip install "decimalai>=0.15", then decimalai skills add dotnet-clr-activation-debugging, and start Claude Code with claude --plugin-dir "$(git rev-parse --show-toplevel)/.agents"

1 · One-time — install the CLI (docs ↗)

pip install "decimalai>=0.15"

2 · Get the skill — writes .agents/skills/dotnet-clr-activation-debugging/ and pins it in .decimal/skills.lock

decimalai skills add dotnet-clr-activation-debugging

No CLI? Get the same file — curl · raw file

curl -fsSL --create-dirs -o .claude/skills/dotnet-clr-activation-debugging/SKILL.md https://app.decimal.ai/s/dotnet-clr-activation-debugging/SKILL.md

Raw file: /s/dotnet-clr-activation-debugging/SKILL.md ↗ · machine-readable summary at /s/dotnet-clr-activation-debugging.json ↗

Safety checks: 3 of 3 passed

Code scan CleanIntent PassedContent Clean

See it in action

One of 6 test cases the skill fixed. Same model, same prompt, with and without the skill.

1 of 6

Prompt

We need to enable CLR activation logging for a single console session without modifying HKEY_LOCAL_MACHINE registry keys across the entire machine. Which environment variable should be configured, and what crucial setup step must be completed beforehand to ensure logs are actually written?

What was checked, without and with the skill
Checked	Without skill	With skill
Identifies COMPLUS_CLRLoadLogDir as the environment variable.	Missed	Passed
States that the target log directory must be created prior to execution.	Passed	Passed

case-07 · gemini-3.6-flash · 9/9/2026 · answers are capped and redacted

What's inside

The instructions your model reads when the skill loads.

SKILL.md284 lines4 files

CLR Activation Debugging

Diagnose .NET Framework runtime activation issues by analyzing CLR activation logs (CLRLoad logs) produced by the shim (mscoree.dll). These logs record every decision the shim makes when selecting and loading a CLR version.

When to Use

A process fails to load the CLR at all ("Unable to find a version of the runtime to use")
The shim picks the wrong CLR version (e.g., v2.0 instead of v4.0)
Unexpected .NET 3.5 Feature-on-Demand (FOD) install dialogs appear
FOD dialogs are expected but do NOT appear
Both CLR v2 and CLR v4 load into the same process, causing failures
A COM object fails to activate because the shim can't resolve the runtime
Legacy hosting APIs (CorBindToRuntime) bind to an unexpected version

When Not to Use

Modern .NET (CoreCLR / .NET 5+) — this skill covers .NET Framework only (the mscoree.dll shim)
Assembly binding failures — use Fusion logs (fuslogvw.exe), not CLR activation logs
Runtime crashes after the CLR has loaded — activation succeeded; the problem is elsewhere

Background

The Shim Architecture

The .NET Framework shim has two layers:

mscoree.dll (the "shell shim") — the public-facing DLL that is the registered InprocServer32 for CLR-hosted COM objects and the entry point for _CorExeMain, legacy APIs, etc.
mscoreei.dll — the actual shim implementation where the runtime selection logic, logging, and activation decisions live. mscoree.dll forwards into mscoreei.dll.

When reading logs, the caller-name:mscoreei.dll in FOD command lines reflects this — it's mscoreei.dll doing the work.

.NET 3.5 / v2.0.50727 Version Mapping

.NET 2.0, 3.0, and 3.5 all share the same CLR runtime version: v2.0.50727. The "3.0" and "3.5" releases were library additions on top of CLR v2.0. For activation purposes, they are all "v2.0.50727." When the shim resolves to v2.0.50727 or FOD offers to install "NetFx3", it's installing the CLR v2.0 runtime (plus the 3.0/3.5 libraries). Similarly, CLR v4.0 (v4.0.30319) covers all .NET Framework versions from 4.0 through 4.8.x.

.NET 3.5 Availability on Recent Windows

On recent Windows versions (Windows 11 Insider Preview Build 27965 and future platform releases), .NET Framework 3.5 is no longer available as a Windows optional component (Feature-on-Demand). It must be installed from a standalone MSI. This means the FOD dialog (fondue.exe /enable-feature:NetFx3) will not succeed on these systems even if it fires. On Windows 10 and Windows 11 through 25H2, FOD remains available. .NET Framework 3.5 reaches end of support on January 9, 2029.

Shim HRESULT Codes

Track record

Benchmark

14 / 17

test cases passed, vs 9 / 17 without

Adoption

Users: 0
Times used: 0

Safety and source details

SkillSafety

✓ 3 of 3 passed

Code scan15 of 15 checks clean

0 critical · 0 warning · 0 info — scanner v5 — 9/8/2026

View 15 scanner checks

live_secretremote_code_executionreverse_shelldata_exfiltrationssrf_metadataagent_snoopinganti_refusaldestructive_commandsobfuscated_unicodeunicode_homoglyphopaque_blobsuspicious_urltool_overreachtrigger_abuseprompt_injection_phrasing

IntentSafe

LLM judge · does the skill do what it claims

ContentClean

LLM judge · policy & harmful-content review

Source

Imported

dotnet / skills

plugins/dotnet-diag/skills/clr-activation-debugging/SKILL.md

View on GitHub ↗

License MITImported 9/8/2026Version v2Bundled 3 files

More skills from the same source and nearby in the registry, with their headline benchmark lift.

Ready to supercharge your AI agents?

See it in action

What's inside

CLR Activation Debugging

When to Use

When Not to Use

Background

The Shim Architecture

.NET 3.5 / v2.0.50727 Version Mapping

.NET 3.5 Availability on Recent Windows

Shim HRESULT Codes

Track record

Benchmark

Adoption

SkillSafety

Source

Related skills