🧩 String Analysis REST API

A RESTful API service that analyzes strings and stores their computed properties such as length, palindrome status, unique character count, word count, SHA-256 hash, and character frequency.

This project demonstrates API design, data validation, and string analysis using modern backend development practices.

📽️ Explainer Overview

This API receives strings, computes analytical properties, and persists them for future retrieval or filtering. It supports querying by computed metrics, natural language filters, and secure hash-based identification.

⚙️ Core Features

For each analyzed string, the API computes and stores the following:

Property	Description
length	Number of characters in the string
is_palindrome	Boolean — true if the string reads the same backward (case-insensitive)
unique_characters	Total number of distinct characters
word_count	Number of words separated by whitespace
sha256_hash	Unique SHA-256 hash of the string
character_frequency_map	Object showing how often each character appears

🧠 API Endpoints

1️⃣ Create / Analyze String

POST /strings

Analyzes and stores a new string.

Request

{
"value": "string to analyze"
}

Success Response — 201 Created

{
"id": "sha256_hash_value",
"value": "string to analyze",
"properties": {
"length": 17,
"is_palindrome": false,
"unique_characters": 12,
"word_count": 3,
"sha256_hash": "abc123...",
"character_frequency_map": {
"s": 2,
"t": 3
}
},
"created_at": "2025-08-27T10:00:00Z"
}

Error Responses

Status	Description
400	Invalid body or missing "value" field
409	String already exists
422	"value" must be of type string

2️⃣ Get Specific String

GET /strings/{string_value}

Retrieve the analysis of a particular string.

Success Response — 200 OK

{
"id": "sha256_hash_value",
"value": "requested string",
"properties": {
/* ... */
},
"created_at": "2025-08-27T10:00:00Z"
}

Error Response

404 String not found

3️⃣ Get All Strings with Filtering

GET /strings

Supports advanced filtering by computed properties.

Example Request

GET /strings?is_palindrome=true&min_length=5&max_length=20&word_count=2&contains_character=a

Success Response — 200 OK

{
"data": [
{
"id": "hash1",
"value": "string1",
"properties": {
/* ... */
},
"created_at": "2025-08-27T10:00:00Z"
}
],
"count": 15,
"filters_applied": {
"is_palindrome": true,
"min_length": 5,
"max_length": 20,
"word_count": 2,
"contains_character": "a"
}
}

Supported Query Parameters

Parameter	Type	Description
is_palindrome	boolean	Filter by palindrome
min_length	integer	Minimum string length
max_length	integer	Maximum string length
word_count	integer	Exact word count
contains_character	string	Character that must appear

Error Response

400 Invalid query parameter types or values

4️⃣ Natural Language Filtering

Use human-like text queries to fetch matching strings.

GET /strings/filter-by-natural-language?query={text}

Example Queries

Query	Parsed Filters
"all single word palindromic strings"	{ word_count: 1, is_palindrome: true }
"strings longer than 10 characters"	{ min_length: 11 }
"strings containing the letter z"	{ contains_character: "z" }
"palindromic strings that contain the first vowel"	{ is_palindrome: true, contains_character: "a" }

Example Success Response — 200 OK

{
"data": [
/* matching strings */
],
"count": 3,
"interpreted_query": {
"original": "all single word palindromic strings",
"parsed_filters": {
"word_count": 1,
"is_palindrome": true
}
}
}

Error Responses

Status	Description
400	Query cannot be parsed
422	Parsed but filters are conflicting

5️⃣ Delete String

DELETE /strings/{string_value}

Removes a stored string and its analysis.

Success Response — 204 No Content

Error Response — 404 String not found

🧱 Suggested Tech Stack

Layer	Technology
Runtime	Node.js (v18+)
Framework	Express.js
Database	MongoDB / Mongoose
Security	Helmet, CORS, Express Rate Limit
Hashing	Node crypto module

🚀 Getting Started

1. Clone Repository

git clone https://github.com/yourusername/string-analysis-api.git
cd string-analysis-api

2. Install Dependencies

npm install

3. Set Up Environment (.env)

PORT=5000
MONGO_URI=mongodb://localhost:27017/string_analysis_db

4. Run Server

npm run dev

5. Test the Endpoints

Use Postman, Insomnia, or cURL to interact with the API.

🧩 Example Workflow

1. POST/strings → Analyze “racecar”

2. GET/strings/racecar → Retrieve its analysis

3. GET/strings?is_palindrome=true → Get all palindromic strings

4. GET/strings/filter-by-natural-language?query=strings longer than 10 characters

5. DELETE/strings/racecar → Remove it

📘 Notes

• The SHA-256 hash acts as both a unique ID and primary key.

• Palindrome check ignores case and whitespace.

• Character frequency map includes spaces and punctuation for completeness.

• Filtering supports combined conditions.

• Natural language parsing may use basic keyword heuristics or a lightweight NLP library.

📄 License

MIT License © 2025 — String Analysis API