Conciseness

The body is a dense rule catalog with no padding: it never explains what F#, C#, or interop are, and every non-obvious statement earns its place (e.g. "F# does not write the nullness of a byref element into the metadata, so C# reads the value as never null"). Project-specific context ("morphir-dotnet writes domain types in F# and keeps the CLI edge in C#") is exactly what Claude could not know otherwise.

Actionability

Guidance is fully executable: a copy-paste `.fsproj` property block, exact member signatures ("static member TryParse(text, out result, out failure) : bool"), exact attribute patterns ("[<Out; MaybeNullWhen(false)>]"), exact commands ("git diff <base>...HEAD -- '*.fs' '*.fsi' '*.fsproj' '*.cs'"), and a ready-to-use subagent prompt with an exact output format ("path:line: rule N: problem. fix."). It is not a score above 5, and it exceeds anchor 4 because concrete examples cover the common cases via references/patterns.md, which the body states compile.

Workflow Clarity

"Before you start" is a clear 3-step sequence with an explicit checkpoint ("Check the project settings (rule 1). Without them, the C# compiler cannot see F# nullness"), and the review workflow ships a full checklist, a severity ordering ("most severe first"), a reporting format, and the no-findings case ("If there is no finding, say so"). Not the level below (4) because a validation checklist and reporting loop are explicitly present, not merely implied.

Progressive Disclosure

The split is clean: rules live in SKILL.md and code examples live in references/patterns.md (verified to exist, 228 lines, one level deep, linking only back to ../SKILL.md). The reference is well signaled twice with read timing ("Read that file before you write new boundary code"), and Related points to repo docs without nesting. Not anchor 4 because there are no organization gaps — navigation and placement are both explicit.

Specificity

The description enumerates nine concrete covered areas — "parsed domain types, nullness metadata, TryParse/Create members, Match members for unions, collections, option and null, equality, ToString and AOT safety, and the .fsproj settings" — which is comprehensive coverage of the niche with no vague filler. Not anchor 4 because the coverage has no gaps: every major boundary concern is named explicitly.

Completeness

Both halves are explicit: what ("Rules for F# code that C# calls, and C# code that calls F#, in morphir-dotnet. Covers ...") and when ("Use when you add or change a public F# type, member or module that a C# project uses; ... or when you review a diff that crosses the F#/C# boundary") plus concrete trigger phrases. This matches the anchor-5 pattern of explicit what + explicit when with concrete triggers, so 4 (where 'when' could be more specific) does not fit.

Trigger Term Quality

Twelve explicit trigger phrases including natural synonyms ("F# interop", "C# interop", "call F# from C#", "F# union in C#") and terms a developer would literally type when hitting this problem ("MaybeNullWhen", "CompiledName", "Nullable enable fsproj", "TryParse", "parse don't validate"). Not anchor 4 because synonyms and tool/file-specific variations are all present.

Distinctiveness Conflict Risk

A clear niche — the F#/C# boundary in a specific repository — with triggers dominated by interop-specific terms ("F# union in C#", "CompiledName", "F# nullness") that would not fire for unrelated skills. A few generic terms ("TryParse", "oblivious") exist but are contextualized by the surrounding interop framing, leaving only minimal conflict risk, which is exactly the anchor-5 condition.