Conciseness

The body is lean and code-first ("Either = success or failure. Right(value) or Left(error)."), assumes Claude's competence, and every section earns its place with no padding or restating of basics.

Actionability

Provides copy-paste-ready, executable TypeScript covering create/transform/extract plus common patterns (validation chain, JSON parse via tryCatch), spanning the typical cases a user would need.

Workflow Clarity

Content is clearly organized into Create/Transform/Extract/Patterns sections and the chained-validation example sequences steps; as a reference card it has no destructive or batch operation requiring explicit validation checkpoints, so it stays just below 5.

Progressive Disclosure

A single self-contained file with well-signaled section headers and no nested references; slightly above 50 lines and all content inline, so it is well-structured but not the cleanest possible split for a 5.

Specificity

Names the domain ("Either type") and concrete use cases (error handling, validation, operations that can fail with typed errors), but describes the artifact as a "quick reference" rather than listing multiple concrete actions, so coverage is not comprehensive.

Completeness

Has both a clear "what" ("Quick reference for Either type") and an explicit "Use when..." clause with concrete triggers; the "what" is somewhat terse, keeping it just below a 5.

Trigger Term Quality

Includes natural terms users would say ("error handling", "validation") plus the more technical "typed errors"; good keyword coverage though a few natural synonyms are missing.

Distinctiveness Conflict Risk

The Either type and fp-ts error-handling niche is a distinct trigger space with minimal conflict risk, though it could marginally overlap with general error-handling skills.