URL Query Parameter Parser & Object Builder
Parse, edit, inspect, and transform URL query strings into JSON, TypeScript interfaces, and encoded URLs client-side.
Query Parameters Editor
Serialized Object & Reconstructed URL
{
"utm_source": "newsletter",
"utm_medium": "email",
"utm_campaign": "spring_launch_2026",
"utm_content": "cta_banner",
"ref_id": "usr_8829",
"experiments": [
"exp_cart_v2",
"exp_dark_mode"
]
}Anatomy of URL Query Strings: RFC 3986 & WHATWG Standards
Uniform Resource Identifiers (URIs) rely on query components to transfer non-hierarchical state across web clients and servers. Governed by RFC 3986 and modern WHATWG specifications, query strings begin with the question mark delimiter (?) and connect sequences of key-value pairs using ampersands (&).
In modern single-page applications (SPAs) and REST APIs, query parameters govern pagination offsets, search filters, analytics tracking (UTM tags), state verification in OAuth 2.0 PKCE handshakes, and feature toggles. Properly isolating, sanitizing, and casting these parameters into type-safe data structures is critical to prevent injection vulnerabilities and state desynchronization.
Component Isolation
Separates protocol schemes, domain paths, query parameters, and anchor fragments (#) to avoid accidental string concatenation bugs.
Type Preservation
Converts raw string literals like "true", "false", "null", and numeric values into strict TypeScript and JSON primitive types.
Collision Resolution
Handles duplicate keys deterministically by aggregating repeated parameters into arrays or selecting explicit first/last overrides.
Percent-Encoding & Reserved Character Matrix
URIs only allow specific US-ASCII characters. Any character outside the unreserved character set (alphanumerics, hyphen, underscore, period, and tilde) must be percent-encoded using its hexadecimal UTF-8 byte representation:
| Character | Hex Encoding | RFC 3986 Role | Common Ingestion Risk |
|---|---|---|---|
| Space (' ') | %20 or + | Whitespace representation | plus-space confusion in form encodings |
| & | %26 | Parameter separator delimiter | Unencoded values split into unwanted parameters |
| = | %3D | Key-value assignment delimiter | Truncates values containing Base64 padding (=) |
| # | %23 | URI fragment delimiter | Cuts off parameters downstream from unencoded hash |
| / | %2F | Path segment separator | Breaks reverse proxy path rewriting rules |
Security Hardening: Query String Parameter Pollution (HPP)
HTTP Parameter Pollution (HPP) occurs when an attacker injects duplicate parameter keys to bypass Web Application Firewall (WAF) filters or alter backend business logic. Different backend web frameworks parse repeated parameters in conflicting ways:
Framework Ingestion Behaviors
- • Express.js / Node.js: Repeated keys default to an array (
["val1", "val2"]), which can trigger unexpected type errors if the code expects a string. - • PHP & Python (Flask): Keep the last parameter value (
val2), ignoring preceding occurrences. - • ASP.NET: Concatenates duplicate values with a comma (
val1,val2).
Parameter Hardening Rules
- • Never expose credentials: Passwords, API tokens, and JWTs should never be transmitted in query parameters, as they are logged in plain text in browser histories, proxy logs, and referer headers.
- • Validate and cast explicitly: Use schema validation libraries (like Zod or Ajv) to verify that incoming query parameters conform strictly to expected data types.
- • Always sanitize redirects: Parameterized
redirect_urivalues must be validated against strict origin whitelists to prevent Open Redirect exploits.
Production Query Parsing in Modern TypeScript & Next.js
Implement bulletproof query parameter deconstruction across client and server environments using native WHATWG URL APIs:
Next.js App Router (Server Component)
interface PageProps {
searchParams: Promise<{ [key: string]: string | string[] | undefined }>;
}
export default async function SearchPage({ searchParams }: PageProps) {
const params = await searchParams;
const query = typeof params.q === 'string' ? params.q : '';
const page = Number(params.page) || 1;
const tags = Array.isArray(params.tag)
? params.tag
: params.tag ? [params.tag] : [];
return <div>Search: {query} (Page {page})</div>;
}Client-Side Web API (URLSearchParams)
export function parseQueryToObject(urlStr: string): Record<string, any> {
const url = new URL(urlStr, "https://dummy.base");
const result: Record<string, any> = {};
url.searchParams.forEach((val, key) => {
if (result[key] !== undefined) {
result[key] = Array.isArray(result[key])
? [...result[key], val]
: [result[key], val];
} else {
result[key] = val;
}
});
return result;
}Frequently Asked Questions (FAQ)
How does the URL Query Parameter Parser handle duplicate parameter keys?
The parser gives you three configurable resolution strategies: Combine into Array (default, creating an array of values for repeated keys such as ?tag=api&tag=v2), Keep Last Occurrence (mirroring standard PHP/Node query string parsers), or Keep First Occurrence.
What is the difference between decodeURI and decodeURIComponent in query strings?
decodeURI is intended for full URLs and preserves reserved delimiters such as ?, &, =, and /. decodeURIComponent decodes individual key or value tokens, properly translating encoded characters such as %20 (spaces), %26 (&), and %3D (=) without breaking the overall URI syntax.
Does this tool upload parsed URLs or authentication parameters to remote servers?
No. The entire query parsing, URL reconstruction, decoding, and JSON/TypeScript serialization occurs purely client-side inside your browser sandbox via native Web APIs (URL and URLSearchParams). No URL parameters or authorization tokens ever leave your machine.
How are boolean and numeric query string values transformed?
When Auto Type Casting is toggled on, strings matching 'true', 'false', 'null', and valid safe integers or floating-point numbers are automatically converted to their native JavaScript/JSON primitives rather than remaining generic strings.
Can I edit query parameters and reconstruct the full encoded URL in real time?
Yes. You can add, toggle, edit, or delete individual keys and values in the interactive table. The tool updates the reconstructed URL, query string, and structured object export immediately.
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