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.NET P/Invoke · dotnet | DecimalAI

codingby dotnet

.NET P/Invoke

dotnet/dotnet-pinvoke

Source dotnet/skills ↗License MIT

Correctly call native (C/C++) libraries from .NET using P/Invoke and LibraryImport. Covers function signatures, string marshalling, memory lifetime, SafeHandle, and cross-platform patterns. USE FOR: writing new P/Invoke or LibraryImport declarations, reviewing or debugging existing native interop code, wrapping a C or C++ library for use in .NET, diagnosing crashes, memory leaks, or corruption at the managed/native boundary. DO NOT USE FOR: COM interop, C++/CLI mixed-mode assemblies, or pure man

SkillScore95Maintained

Automatic

Coding pack

Last verified 8/9/2026

What it changes

Passed 21 of 22 test cases with the skill, and 14 of 22 without it.

Without skill64%

With skill95%

Checks it passed that the model alone missed

The interop method parameter uses Span or ReadOnlySpan
The method declaration sets SetLastPInvokeError to true
The P/Invoke declaration sets SetLastPInvokeError to true

and 4 more in the full report

7 fixed14 passed either way1 still failing0 broke

Pass-rate lift: +32 pp
Tokens: +171%
Agent turns: 0%
Response time: -15%

Model gemini-3.6-flashMeasured 8/9/2026v121 of 22 cases passed with skill

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-dotnet-pinvoke/SKILL.md https://app.decimal.ai/s/dotnet-dotnet-pinvoke/SKILL.md

Want it pinned and updatable? pip install "decimalai>=0.15", then decimalai skills add dotnet-dotnet-pinvoke, 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-dotnet-pinvoke/ and pins it in .decimal/skills.lock

decimalai skills add dotnet-dotnet-pinvoke

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

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

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

Safety checks: 3 of 3 passed

Code scan CleanIntent PassedContent Clean

See it in action

One of 7 test cases the skill fixed. Same model, same prompt, with and without the skill.

1 of 7

Prompt

I am writing a `LibraryImport` declaration in .NET 8 for the Windows API function `GetModuleFileNameW`. What string marshalling options should be configured on the attribute?

What was checked, without and with the skill
Checked	Without skill	With skill
The LibraryImport attribute sets StringMarshalling to StringMarshalling.Utf16	Passed	Passed
The method declaration sets SetLastPInvokeError to true	Missed	Passed

case-06 · gemini-3.6-flash · 8/9/2026 · answers are capped and redacted

What's inside

The instructions your model reads when the skill loads.

SKILL.md435 lines3 files

.NET P/Invoke

Calling native code from .NET is powerful but unforgiving. Incorrect signatures, garbled strings, and leaked or freed memory are the most common sources of bugs — all can manifest as intermittent crashes, silent data corruption, or access violations far from the actual defect.

This skill covers both DllImport (available since .NET Framework 1.0) and LibraryImport (source-generated, .NET 7+). When targeting .NET Framework, always use DllImport. When targeting .NET 7+, prefer LibraryImport for new code. When native AOT is a requirement, LibraryImport is the only option.

When to Use This Skill

Writing a new [DllImport] or [LibraryImport] declaration from a C/C++ header
Reviewing P/Invoke signatures for correctness (type sizes, calling conventions, string encoding)
Wrapping an entire C library for use from .NET
Debugging AccessViolationException, DllNotFoundException, or silent data corruption at the native boundary
Migrating DllImport declarations to LibraryImport for AOT/trimming compatibility
Diagnosing memory leaks or heap corruption involving native handles or buffers

Stop Signals

Single function? Map the signature (Steps 1-3), handle strings/memory only if relevant, skip tooling and migration sections.
Don't migrate existing DllImport to LibraryImport unless the user asks or AOT/trimming is an explicit requirement.
Don't recommend CsWin32 unless the target is specifically Win32 APIs.
Don't generate callbacks (Step 8) unless the native API requires function pointers.
Review request? Use the validation checklist — don't rewrite working code.

Inputs

Input	Required	Description
Native header or documentation	Yes	C/C++ function signatures, struct definitions, calling conventions
Target framework	Yes	Determines whether to use `DllImport` or `LibraryImport`
Target platforms	Recommended	Affects type sizes (`long`, `size_t`) and library naming
Memory ownership contract	Yes	Who allocates and who frees each buffer or handle

Agent behavior: When documentation and native headers diverge, always trust the header. Online documentation (including official Win32 API docs) frequently omits or simplifies details about types, calling conventions, and struct layout that are critical for correct P/Invoke signatures.

Workflow

Step 1: Choose DllImport or LibraryImport

Track record

Benchmark

21 / 22

test cases passed, vs 14 / 22 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 v4 — 8/3/2026

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-advanced/skills/dotnet-pinvoke/SKILL.md

View on GitHub ↗

License MITImported 8/3/2026Version v1Bundled 2 files

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

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See it in action

What's inside

.NET P/Invoke

When to Use This Skill

Stop Signals

Inputs

Workflow

Step 1: Choose DllImport or LibraryImport

Track record

Benchmark

Adoption

SkillSafety

Source

Related skills