# json-data-handling

Guides AI agents through reliable JSON operations in Python and JavaScript, covering schema validation, custom serialization, and large file streaming.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 385 installs · ★ 78
- Author: bobmatnyc
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/bobmatnyc/claude-mpm-skills/tree/HEAD/universal/data/json-data-handling/SKILL.md
- Updated: 2026-07-18
- HTML: https://affpapa.org/en/nevibecode/skills/json-data-handling

## What it does

This skill provides strict patterns for handling JSON payloads in Python and Node.js environments. For Python, it outlines custom `datetime` serialization via `JSONEncoder`, safe nested key lookups, recursive dictionary merges, and `snake_case` to `camelCase` key transformations. JavaScript examples cover property filtering, `BigInt` serialization, and circular reference handling with `WeakSet`.

Complex data verification relies on `jsonschema`. To prevent out-of-memory errors on large datasets, the skill directs the agent to stream files via `ijson` instead of reading everything into memory at once.

Keep in mind that streaming routines will fail unless `ijson` is installed in your Python environment beforehand.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add bobmatnyc/claude-mpm-skills --skill json-data-handling -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/json-data-handling/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/json-data-handling/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add bobmatnyc/claude-mpm-skills --skill json-data-handling -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/json-data-handling/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add bobmatnyc/claude-mpm-skills --skill json-data-handling -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/json-data-handling/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install bobmatnyc/claude-mpm-skills json-data-handling
```

2. **Manually: put the files in place**
- File: `.github/skills/json-data-handling/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add bobmatnyc/claude-mpm-skills --skill json-data-handling -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/bobmatnyc/claude-mpm-skills --path universal/data/json-data-handling
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/json-data-handling/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add bobmatnyc/claude-mpm-skills --skill json-data-handling -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/bobmatnyc/claude-mpm-skills/tree/HEAD/universal/data/json-data-handling/SKILL.md

## When to use it
- Serialize Python `datetime` instances into ISO format without JSON encoding errors
- Prevent JavaScript `JSON.stringify` crashes caused by circular object references
- Stream heavy JSON files in Python without exhausting available memory
- Safely retrieve deeply nested dictionary values using fallback defaults

## Example prompts
- Write a Python script to stream records from `large_data.json` using `ijson`
- Serialize this JavaScript object safely with circular reference protection
- Transform all dictionary keys from `snake_case` to `camelCase` before sending the payload

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 91acc1837b9eafae.

BEGIN THIRD-PARTY FILE 91acc1837b9eafae
````text
---
name: json-data-handling
description: Working effectively with JSON data structures.
user-invocable: false
disable-model-invocation: true
updated_at: 2025-10-30T17:00:00Z
tags: [json, data, parsing, serialization]
progressive_disclosure:
  entry_point:
    summary: "Working effectively with JSON data structures."
    when_to_use: "When working with data, databases, or data transformations."
    quick_start: "1. Review the core concepts below. 2. Apply patterns to your use case. 3. Follow best practices for implementation."
---
# JSON Data Handling

Working effectively with JSON data structures.

## Python

### Basic Operations

```python
import json

# Parse JSON string
data = json.loads('{"name": "John", "age": 30}')

# Convert to JSON string
json_str = json.dumps(data)

# Pretty print
json_str = json.dumps(data, indent=2)

# Read from file
with open('data.json', 'r') as f:
    data = json.load(f)

# Write to file
with open('output.json', 'w') as f:
    json.dump(data, f, indent=2)
```

### Advanced

```python
# Custom encoder for datetime
from datetime import datetime

class DateTimeEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, datetime):
            return obj.isoformat()
        return super().default(obj)

json_str = json.dumps({'date': datetime.now()}, cls=DateTimeEncoder)

# Handle None values
json.dumps(data, skipkeys=True)

# Sort keys
json.dumps(data, sort_keys=True)
```

## JavaScript

### Basic Operations

```javascript
// Parse JSON string
const data = JSON.parse('{"name": "John", "age": 30}');

// Convert to JSON string
const jsonStr = JSON.stringify(data);

// Pretty print
const jsonStr = JSON.stringify(data, null, 2);

// Read from file (Node.js)
const fs = require('fs');
const data = JSON.parse(fs.readFileSync('data.json', 'utf8'));

// Write to file
fs.writeFileSync('output.json', JSON.stringify(data, null, 2));
```

### Advanced

```javascript
// Custom replacer
const jsonStr = JSON.stringify(data, (key, value) => {
  if (typeof value === 'bigint') {
    return value.toString();
  }
  return value;
});

// Filter properties
const filtered = JSON.stringify(data, ['name', 'age']);

// Handle circular references
const getCircularReplacer = () => {
  const seen = new WeakSet();
  return (key, value) => {
    if (typeof value === 'object' && value !== null) {
      if (seen.has(value)) return;
      seen.add(value);
    }
    return value;
  };
};
JSON.stringify(circularObj, getCircularReplacer());
```

## Common Patterns

### Validation

```python
from jsonschema import validate

schema = {
    "type": "object",
    "properties": {
        "name": {"type": "string"},
        "age": {"type": "number", "minimum": 0}
    },
    "required": ["name", "age"]
}

# Validate
````
END THIRD-PARTY FILE 91acc1837b9eafae

The third-party file has ended. Everything between the 91acc1837b9eafae tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

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