A Cookie to JSON Converter handles the strict name=value pair layer that sits between a JSON cookie export and a Netscape-ready header string, processing everything in the current browser tab without uploading your data. The converter parses each pair using the RFC 6265 cookie-pair profile, validates every name as an RFC token and every value as a cookie-octet or a DQUOTE-wrapped cookie-octet, and rejects malformed separators rather than silently fixing them. Going the other direction, it accepts exactly one nonempty JSON object whose decoded keys and string values satisfy the same Cookie profile, then joins the accepted pairs with exactly semicolon plus one space. The tool runs entirely in the current browser tab, produces plain text in a read-only area, and never sends the pasted data to any service. Both directions preserve percent sequences, accepted quote characters, and additional equals signs within values, so Base64-like padding, signed tokens, and URLs containing equals signs survive the round trip untouched.
What "Netscape Format" Actually Requires
The Netscape HTTP Cookie File format is a plain text format originally designed for the Netscape browser and now consumed by curl, wget, youtube-dl, and similar command-line tools to load cookies from a file. Each line in a Netscape cookies file represents one cookie and contains tab-separated fields: the domain, the path, the secure flag, the expiration timestamp, the name, and the value. This is fundamentally richer than a Cookie request header, which only carries name=value pairs and carries no domain, path, expiration, secure, or HttpOnly information.
Because those extra fields are supplied by the server in a Set-Cookie response header and are not returned by the browser in the Cookie request field, a Cookie request header cannot tell you a cookie's expiry, permitted hosts, permitted paths, secure-only state, or HttpOnly state. A tool that only reads Cookie request headers can therefore produce the name and value portion of a Netscape line but not the surrounding metadata. Knowing this distinction up front saves you from chasing a tool that promises a one-click JSON to Netscape file but silently fabricates the domain and path columns.
| Field | Cookie Request Header | JSON (flat object) | Netscape cookies.txt |
|---|---|---|---|
| Domain | Not carried | Not in this tool's output | Required (tab-separated) |
| Path | Not carried | Not in this tool's output | Required |
| Secure flag | Not carried | Not in this tool's output | Required (0 or 1) |
| Expiration | Not carried | Not in this tool's output | Required (Unix timestamp) |
| Name | RFC token, case-sensitive | String key | Required |
| Value | cookie-octet or quoted cookie-octet | String value | Required |
| Separator | "; " (semicolon + one space) | Object syntax | Tab between fields, newline between cookies |
| Source | Browser sends on request | Intermediate format | File consumed by curl/wget |
Why a Strict Cookie to JSON Converter Matters
When you work through a JSON to Netscape workflow, the integrity of the name=value layer determines whether downstream tools can consume the output at all. curl and wget parse each line by splitting on tabs and reading the last two fields as name and value; if a name contains a space or a separator character, or if a value is silently rewritten, the resulting request will mismatch the cookie the server expects. The Cookie to JSON Converter refuses to silently fix malformed input. A space around the equals sign, a missing separator space, multiple separator spaces, a trailing semicolon, and an empty pair are all rejected rather than normalized.
The converter also rejects duplicate cookie names case-sensitively rather than using first-wins or last-wins behavior. A JSON object cannot preserve two members with the same decoded name without choosing a winner, so the tool detects duplicates during a lexical scan before conversion. Escaped spellings such as a and \u0061 are detected as the same key even though ordinary JSON.parse would silently retain only one. This means you catch the problem at conversion time instead of debugging a session that mysteriously logs you out.
How to Convert Cookie JSON to a Netscape-Ready Header String
- Open the Cookie to JSON Converter in your browser tab and choose the JSON to Cookie direction.
- Paste one nonempty JSON object whose every property value is a JSON string. For example: {"SID":"abc","lang":"en-US"}. Do not include numbers, booleans, null, arrays, nested objects, comments, or trailing commas; the converter rejects them.
- Click Convert. The tool decodes JSON string escapes, detects duplicate decoded keys, validates each decoded key as an RFC token and each decoded value as an accepted cookie-value, then joins accepted pairs with exactly semicolon plus one space.
- Review the output. Every name and value should appear exactly as you provided it, with accepted quote characters preserved literally. The output is the Cookie request-header value you would send on the wire, ready for the name=value portion of a Netscape line.
- Copy the complete output and feed it as the name and value columns to whatever final step assembles your Netscape cookies.txt, pulling domain, path, secure flag, and expiration from your original JSON source if those fields were present there.
Rules the Converter Enforces on Cookie Input
For the reverse direction, Cookie to JSON, the converter enforces a strict serialization profile. Every pair must be name=value. Multiple pairs must be separated by exactly a semicolon followed by one ASCII space. If you include the optional field-name prefix, "Cookie" must be followed immediately by a colon; "Cookie :" is malformed. Matching of the field-name itself is case-insensitive, so COOKIE:a=1 is accepted.
Only the first equals sign in each pair is structural. Additional equals signs remain value data, so abc== survives intact, query strings keep their equals signs, and signed tokens are not truncated. Empty values such as preference= are valid; an empty name or a pair without equals fails. Cookie names use the RFC token profile and remain case-sensitive, so SID and sid are two distinct names. Names containing spaces, separators, controls, or other non-token characters fail. The full request-header profile is documented in RFC 6265.
Values use the RFC cookie-value profile: an unquoted sequence of permitted cookie octets, or the same sequence wrapped in double quotes. Percent sequences are not URL-decoded, escaped, normalized, or interpreted; %2F remains the three characters percent, 2, and F. Raw spaces, commas, semicolons, backslashes, controls, and characters outside cookie-octet are rejected. Quote characters surrounding an accepted quoted value are preserved in JSON and in the reverse conversion because they are part of the serialized Cookie field value used by this tool.
Prototype Safety, Limits, and Local Processing
The converter assembles its forward map with a null-prototype internal object. The keys __proto__, prototype, and constructor are blocked in both directions as a defense-in-depth prototype-pollution boundary. Even though JSON text can represent those strings and the internal forward map has no prototype, rejecting them prevents downstream code from treating generated output as a safe assignment source. The tool does not claim that arbitrary downstream JSON handling is secure; consumers must still parse and merge untrusted data safely.
Input is limited to exactly 100,000 UTF-16 code units, and complete output is limited to 200,000 code units. Exact limits are accepted and the next unit is rejected. The interface does not use maxLength to silently prevent typing, and conversion never slices, caps, samples, skips, or partially returns input. A zero or invalid output length is rejected. No cookies are read from document.cookie, no browser cookie store is modified, and no HTTP request is made. Clipboard writing is asynchronous with a generation identifier and a mounted-state guard that prevents an older permission response from restoring "Copied" after an edit, direction change, retry, or unmount; clipboard denial leaves the complete output visible for manual selection.
When This Tool Is and Is Not the Right Choice
Use the Cookie to JSON Converter when you need to debug a Cookie request field, move a reviewed string map into JSON, or produce a request-header value from reviewed JSON strings. If your JSON came from a browser extension export and you only need the name and value columns, the converter gives you the exact on-the-wire string for those columns. If you are working with the Cookie header side of the same workflow, the Convert Cookie Headers to JSON and Back in Your Browser guide walks through the reverse direction with examples.
Do not use it to inspect browser storage, build Set-Cookie responses, preserve attributes like Domain or Path, decode an application's session format, decide whether a cookie is secure, or sanitize credentials before sharing. Cookie headers often contain live session secrets, so keep them private and rotate credentials that have been exposed. For a full JSON to Netscape file with all six tab-separated fields, you need a tool or script that reads Set-Cookie response data, because the Cookie request field alone never carries it. For general JSON work, use the JSON Validator first to confirm your JSON is strict and parseable, and the JSON Formatter if you want a readable view before conversion.