YAML Agent Skill

YAML wire format for json-render with streaming parser, prompt generation, and AI SDK transform. Use when working with @json-render/yaml, YAML-based spec streaming, yaml-spec/yaml-edit fences, or YAML prompt generation.

1k tokens

context cost

the whole folder, loaded on every use

files

instructions only

copies elsewhere

how many repositories repackaged it

15821

stars on the repo

on the repository, not the skill itself

Install

one command, takes just this skill from the repository

npx skills add https://github.com/vercel-labs/json-render --skill yaml

The instruction itself

8 sections, as written by the author

@json-render/yaml

YAML wire format for @json-render/core. Progressive rendering and surgical edits via streaming YAML.

Key Concepts

YAML wire format: Alternative to JSONL that uses code fences (yaml-spec, yaml-edit, yaml-patch, diff)
Streaming parser: Incrementally parses YAML, emits JSON Patch operations via diffing
Edit modes: Patch (RFC 6902), merge (RFC 7396), and unified diff
AI SDK transform: TransformStream that converts YAML fences into json-render patches

Generating YAML Prompts

import { yamlPrompt } from "@json-render/yaml";
import { catalog } from "./catalog";

// Standalone mode (LLM outputs only YAML)
const systemPrompt = yamlPrompt(catalog, {
  mode: "standalone",
  editModes: ["merge"],
  customRules: ["Always use dark theme"],
});

// Inline mode (LLM responds conversationally, wraps YAML in fences)
const chatPrompt = yamlPrompt(catalog, { mode: "inline" });

Options:

system (string) — Custom system message intro
mode ("standalone" | "inline") — Output mode, default "standalone"
customRules (string[]) — Additional rules appended to prompt
editModes (EditMode[]) — Edit modes to document, default ["merge"]

AI SDK Transform

Use pipeYamlRender as a drop-in replacement for pipeJsonRender:

import { pipeYamlRender } from "@json-render/yaml";
import { createUIMessageStream, createUIMessageStreamResponse } from "ai";

const stream = createUIMessageStream({
  execute: async ({ writer }) => {
    writer.merge(pipeYamlRender(result.toUIMessageStream()));
  },
});
return createUIMessageStreamResponse({ stream });

For multi-turn edits, pass the previous spec:

pipeYamlRender(result.toUIMessageStream(), {
  previousSpec: currentSpec,
});

The transform recognizes four fence types:

yaml-spec — Full spec, parsed progressively line-by-line
yaml-edit — Partial YAML deep-merged with current spec (RFC 7396)
yaml-patch — RFC 6902 JSON Patch lines
diff — Unified diff applied to serialized spec

Streaming Parser (Low-Level)

import { createYamlStreamCompiler } from "@json-render/yaml";

const compiler = createYamlStreamCompiler<Spec>();

// Feed chunks as they arrive from any source
const { result, newPatches } = compiler.push("root: main\n");
compiler.push("elements:\n  main:\n    type: Card\n");

// Flush remaining data at end of stream
const { result: final } = compiler.flush();

// Reset for next stream (optionally with initial state)
compiler.reset({ root: "main", elements: {} });

Methods: push(chunk), flush(), getResult(), getPatches(), reset(initial?)

Edit Modes (from @json-render/core)

The YAML package uses the universal edit mode system from core:

import { buildEditInstructions, buildEditUserPrompt } from "@json-render/core";
import type { EditMode } from "@json-render/core";

// Generate edit instructions for YAML format
const instructions = buildEditInstructions({ modes: ["merge", "patch"] }, "yaml");

// Build user prompt with current spec context
const userPrompt = buildEditUserPrompt({
  prompt: "Change the title to Dashboard",
  currentSpec: spec,
  config: { modes: ["merge"] },
  format: "yaml",
  serializer: (s) => yamlStringify(s, { indent: 2 }).trimEnd(),
});

Fence Constants

For custom parsing, use the exported constants:

import {
  YAML_SPEC_FENCE,   // "```yaml-spec"
  YAML_EDIT_FENCE,   // "```yaml-edit"
  YAML_PATCH_FENCE,  // "```yaml-patch"
  DIFF_FENCE,        // "```diff"
  FENCE_CLOSE,       // "```"
} from "@json-render/yaml";

Key Exports

| Export | Description |

|--------|-------------|

| yamlPrompt | Generate YAML system prompt from catalog |

| createYamlTransform | AI SDK TransformStream for YAML fences |

| pipeYamlRender | Convenience pipe wrapper (replaces pipeJsonRender) |

| createYamlStreamCompiler | Streaming YAML parser with patch emission |

| YAML_SPEC_FENCE | Fence constant for yaml-spec |

| YAML_EDIT_FENCE | Fence constant for yaml-edit |

| YAML_PATCH_FENCE | Fence constant for yaml-patch |

| DIFF_FENCE | Fence constant for diff |

| FENCE_CLOSE | Fence close constant |

| diffToPatches | Re-export: object diff to JSON Patch |

| deepMergeSpec | Re-export: RFC 7396 deep merge |

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How to use it

Copy the folder

Take vercel-labs/yaml from the repository into ~/.claude/skills for personal use, or into .claude/skills inside a project.

Check the name does not clash

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