Paste any text, response body, or HTTP payload to hash
Ready to generate
Paste your payload and click Generate ETag// generate strong & weak etag hashes instantly
Generate strong or weak ETag hashes from pasted text or HTTP payloads. Supports MD5, SHA-1, SHA-256 and CRC32. Free, browser-based, no upload needed.
Ready to generate
Paste your payload and click Generate ETagEnter any response body, JSON, text, or HTTP content into the input field.
Select Strong or Weak ETag, then pick your hashing algorithm: SHA-256, SHA-1, MD5, or CRC32.
Click Generate to get your ETag value and ready-to-use HTTP header string.
An ETag (Entity Tag) is an HTTP response header used for cache validation. Servers include an ETag in responses; clients send it back via If-None-Match to check if the resource has changed. Strong ETags require byte-for-byte equality; Weak ETags (prefixed W/) allow semantically equivalent responses.
A strong ETag requires the resource to be byte-for-byte identical for a cache hit. A weak ETag (prefixed with W/) signals that two responses are semantically equivalent even if not identical — for example, gzip vs identity encoding of the same content. Weak ETags cannot be used with If-Match in range requests.
SHA-256 is the most secure and collision-resistant option, recommended for modern APIs. SHA-1 is common in legacy systems. MD5 is fast and widely supported but cryptographically broken — fine for cache validation but not security-critical use. CRC32 is extremely fast and compact, often used for large binary files or low-security scenarios.
ETags enable conditional HTTP requests. When a browser or API client has a cached response, it sends the ETag back via If-None-Match. If the resource hasn't changed, the server responds with 304 Not Modified and no body — saving bandwidth and reducing latency significantly for repeat visitors.
Yes — paste the text content of any file into the input. For binary files, you'd typically hash the raw bytes server-side, but for text-based files (HTML, JSON, CSS, JS), pasting the content here will produce the same hash your server would generate using the same algorithm.
No. This tool processes everything in your browser using the Web Crypto API and client-side JavaScript. Your payload never leaves your machine. For very large payloads you can also use the PHP API endpoint included with the tool, which processes server-side without storing any data.
In Nginx, ETags are enabled by default for static files via the etag on; directive. For dynamic responses, use add_header ETag "your-value"; in a location block. In Apache, the FileETag directive controls ETag generation; use Header set ETag "your-value" for dynamic content.
An ETag (Entity Tag) is an HTTP response header field that provides a unique identifier for a specific version of a resource at a URL. Defined in RFC 9110, ETags are one of the most powerful tools in the HTTP caching toolkit, enabling conditional requests that can dramatically reduce bandwidth consumption and latency for both APIs and web applications.
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When a server responds to a request, it can include an ETag header with a unique value representing the current state of the resource. On subsequent requests, the client sends this value back in an If-None-Match header. If the resource hasn't changed, the server returns a 304 Not Modified response with no body — saving the cost of retransmitting the full payload.
This flow is known as a conditional GET request. It's especially valuable for JSON APIs returning large datasets, single-page applications loading static assets, and CDNs validating cached content at edge nodes.
The HTTP specification defines two types of ETags:
"abc123" — guarantee byte-for-byte equality. Two resources with the same strong ETag are completely identical. Strong ETags are required when using If-Match for range requests and partial content (206 Partial Content).W/"abc123" — indicate that two resources are semantically equivalent even if not byte-identical. For example, the same JSON body with or without gzip compression. Weak ETags are appropriate when minor structural differences don't affect the logical content.The ETag specification doesn't mandate any particular hashing algorithm — it only requires the value to be opaque and unique. In practice, common choices include:
In REST APIs, ETags serve two important roles beyond simple caching. First, they enable optimistic concurrency control: clients read a resource and receive its ETag; when updating, they send If-Match: "etag-value" — if another client modified the resource in the meantime, the server returns 412 Precondition Failed, preventing lost updates. This is particularly valuable in collaborative editing systems and multi-instance microservice architectures.
Second, ETags improve API efficiency for polling patterns. Clients repeatedly checking for updates send If-None-Match, and the server returns 304 when nothing has changed — reducing CPU load on both client and server compared to always returning the full payload.
For static files, web servers (Nginx, Apache, IIS) generate ETags automatically, typically based on file size and last-modified timestamp. For dynamic content generated by application code, you need to compute the ETag yourself. The standard approach is to hash the serialized response body:
ETag response header to the quoted hashIf-None-Match against the computed ETag before rendering the full responseThis tool lets you compute that ETag offline — paste your sample response body, choose your algorithm, and get the exact ETag value your server should produce.
ETags have some well-known gotchas in production deployments. The classic problem is multi-server inconsistency: if your servers generate ETags based on internal state (inode numbers, timestamps) rather than content, different servers in a load-balanced cluster will produce different ETags for the same content, defeating caching entirely. Always compute ETags from content hashes when running multiple instances.
Another consideration is ETag and compression: if you serve gzip or Brotli compressed responses, the compressed body has a different hash than the uncompressed body. Use weak ETags when content negotiation may alter the encoding, or compute ETags from the pre-compression content and use the Vary: Accept-Encoding header to ensure cache correctness.
Finally, be mindful of ETag granularity. ETags work at the resource URL level. For APIs returning collections, decide whether the ETag represents the entire collection state (simple but conservative) or individual item states (complex but allows fine-grained caching). Most implementations hash the full response body, which naturally accounts for any change in any item within the collection.