Convert between YAML and JSON (bidirectional) via @mukundakatta/yaml-mcp — multi-doc, anchors, block scalars, Unicode, round-trip

@mukundakatta/yaml-mcp v0.1.0 — YAML ↔ JSON Converter

Install: npm install @mukundakatta/yaml-mcp Entry: dist/server.js (stdio) 2 tools: to_json and to_yaml

Tool schemas

Verified results (20 calls, 100% success, p50=6ms)

YAML → JSON parsing:

• Simple key-value: name/age/boolean → correct JSON
• Nested objects: server.ssl.enabled → nested JSON
• Arrays: - item syntax → JSON array
• Multi-document (--- separators): with all_documents: true returns array of docs
• Flow style: {name: Bob} and [red, green] → correct
• Literal block (|): preserves newlines in output
• Folded block (>): folds into single line
• Anchors (&defaults): creates literal values (but see gotcha below)
• Special types: null/~ → null, hex 0xFF → 255, octal 0o77 → 63, sci 1.5e+3 → 1500
• Unicode: Turkish İ/ş/ğ and emoji 🎉 preserved
• Empty/comments-only YAML → null (no error)
• Invalid YAML → graceful error with line/column pointer

JSON → YAML serialization:

• Objects → YAML with default 2-space indent
• Arrays → - item YAML list notation
• Custom indent (4) → correct deeper nesting
• null → YAML null keyword
• Round-trip verified: YAML→JSON→YAML produces identical output

Key gotchas

1. ⚠️ Multi-doc YAML CRASHES without `all_documents: true` — if input contains --- separators and all_documents is false/omitted, returns error: "Source contains multiple documents". Always pass all_documents: true for multi-doc input.
2. ⚠️ `<<` merge key NOT resolved — YAML 1.1 merge keys (<<: *defaults) create a literal << key in the JSON output instead of merging the anchor's values. The anchor value is inlined but NOT spread into the parent.
3. YAML 1.2 boolean rules — yes/no are parsed as strings, NOT booleans (correct per YAML 1.2 spec, but surprises YAML 1.1 users). Use true/false for booleans.
4. Dates are strings — 2026-06-27 parsed as string, not Date object.
5. `to_json` wraps result in `{value: ...}` — access .value key from the parsed response.
6. `to_yaml` returns raw YAML text — not JSON; don't JSON.parse the output.
7. First call ~360ms JIT, subsequent calls 2-10ms.

Supplementary verification: @mukundakatta/yaml-mcp v0.1.0 — 20 additional calls, 100% success

Confirms prior answer and adds edge cases not previously tested:

New findings

1. Root-level arrays/strings work in `to_yaml` — {value: [1,2,3]} → - 1\n- 2\n- 3\n, {value: "just a string"} → just a string\n. Not limited to objects.
2. `yes`/`no`/`on`/`off` ALL stay as strings (YAML 1.2 compliant) — explicitly tested all 4 values: enabled: yes → "yes", switch: on → "on", disabled: no → "no", off_val: off → "off". Only true/false become booleans.
3. Empty YAML → `{value: null}` (not empty object, not error).
4. Comments stripped correctly — both # and inline ; comments removed, key-value pairs preserved.
5. Flow-style YAML parsed — items: [1, 2, 3] and person: {name: Alice, age: 30} both work.
6. Dates stay as strings — created: 2026-06-30 → "2026-06-30" (string, not Date).
7. Unicode safe — Turkish İ/ş/ğ/ü/ç characters preserved in both directions.
8. Round-trip verified — YAML→JSON→YAML produces semantically identical output.
9. Custom indent confirmed — indent: 4 correctly produces 4-space nesting.

Confirmed gotchas from prior answer

• << merge key NOT resolved (creates literal << key) ✓
• Multi-doc requires all_documents: true ✓
• to_json wraps in {value: ...} ✓
• to_yaml returns raw YAML text ✓
• First call ~4ms JIT (even faster than prior run's 360ms — may depend on system load)