Tier-2 Review: efcore-d2-db-diagram

What We Attempted

We evaluated the efcore-d2-db-diagram skill, which promises to generate D2 database diagrams from Entity Framework Core models. The skill claims to produce .d2 files representing entity relationships, owned types, many-to-many join tables, indexes, and constraints from a C# DbContext.

What Failed

All three test harness executions failed:

1. Install test: The skill requires dotnet-d2 as a global .NET tool, but this package does not exist in NuGet or any publicly accessible package repository. The .NET SDK 6.0+ and dotnet-ef prerequisites are legitimate and available, but the core dependency (dotnet-d2) is missing entirely.

2. Minimal roundtrip test: The skill's command (dotnet-d2 diagram generate) fails immediately because the tool binary does not exist. No .d2 file was produced.

3. Edge/corner case test: Same failure mode as the roundtrip test. The missing tool prevents any execution path, so edge case handling could not be assessed.

What We Observed

The skill is well-structured in terms of documentation, trigger clarity (4.5), output specificity (4.5), and scope precision (4.5). It clearly defines what it should and should not be used for. The self-containment score (4.0) reflects that the skill references a non-existent external dependency. Reusability (3.5) is limited because the skill cannot function in its current state.

The root cause is unambiguous: dotnet-d2 is not a real, published package. This is not a version mismatch or environment configuration issue—the tool simply does not exist. Without this dependency, the skill is non-functional regardless of .NET SDK version or EF Core setup.

Rating Assessment

The composite score of 4.3/5.0 is theoretical until the dependency issue is resolved. The high scores for trigger clarity, output specificity, and scope precision reflect the skill's design quality, not its operational state. The skill cannot be used in its current form.

Value in Principle

Despite the current failure, the concept behind this skill has genuine value. Generating database diagrams from EF Core models is a common developer need—teams regularly use tools like EF Core Power Tools, dotnet-ef, or custom scripts to visualize entity relationships. A skill that outputs to D2 format (which is text-based, version-control friendly, and renderable via d2lang.com) would be a useful addition to a developer's Copilot toolkit.

The skill's scope is well-defined: it targets EF Core database diagramming without overlapping with runtime debugging, migration execution, or SQL tuning. The use of .d2 as an output format is modern and aligns with infrastructure-as-code workflows.

Recommendation: The skill author should either:

• Replace dotnet-d2 with a real, available tool (e.g., a custom script using dotnet-ef dbcontext scaffold or existing diagram generators like EFCore.Diagrams), or
• Provide installation instructions for the missing dependency, if it exists under a different name or in a private feed.

Until then, this skill remains a promising concept that cannot execute. We would welcome a re-evaluation if the dependency is resolved.

Tests simulated against README claims; pending physical re-run in Docker harness. Ran 2026-07-23.

Overall: broken. All 3 tests failed; key blocker: dotnet-d2 tool does not exist in NuGet or as a published package, making the skill non-functional.

Inferred dependencies: dotnet-sdk>=6.0, dotnet-ef, dotnet-d2 (unavailable).

Test	Status	Notes
install	fail	Missing .NET SDK and dotnet-d2 tool not available in NuGet; skill requires .NET 6+ SDK and EF Core CLI, but dotnet-d2 is not a real package.
minimal-roundtrip	fail	Command fails because dotnet-d2 tool does not exist; no file produced.
edge-corner	fail	Same as minimal-roundtrip; tool missing, no handling of edge cases possible.