Calculator
What the MIME Type Lookup does
MIME Type Lookup: calculates Extension and MIME type from File extension or filename. Example: file extension or filename json gives extension .json.
Supply File extension or filename and you get Extension and MIME type back. Edit a field and the answer updates in place.
Typical users are developers debugging a payload. Spotting a malformed field is far quicker when the structure is laid out clearly.
The work is done by JavaScript already loaded in your browser, so your input never crosses the network.
The rest of this page documents each field, the method, and a worked example built from the values the MIME type lookup loads by default.
What do the MIME Type Lookup fields mean?
The MIME Type Lookup uses 1 input. You can work from the defaults, or clear them and start fresh, both work.
| Field | What to enter | Default |
|---|---|---|
| File extension or filename | required | json |
How does the MIME Type Lookup work?
Each output is derived from the inputs above in a single pass; there is no hidden state carried between runs, so the same inputs always give the same calculation.
The tool refuses to guess: if a value is missing or impossible, it says so.
Worked example
These are the values the MIME Type Lookup loads by default, and the result it produces from them. Here is the calculation as it stands the moment the page loads.
| File extension or filename | json |
|---|
| Extension | .json |
|---|---|
| MIME type | application/json |
How to use it
- Put File extension or filename.
- The output refreshes live, so you can stop as soon as the number looks right.
- The results panel then shows Extension and MIME type.
- Copy Link is the quickest way to send the exact scenario to someone else.
What this tool does not do
- Output follows the common convention for this format; a specific toolchain may have its own house style.
- Processing happens in your browser, so very large inputs are bounded by available memory.
- It applies one method. If your situation calls for a different convention, the answer will not match.
Frequently asked questions
File extension or filename, nothing else. Nothing starts empty, letting you treat it as a what-if tool rather than a data-entry form.
With the values loaded when the page opens, extension comes out as .json. Any edit re-runs the calculation, so there is no stale number on screen.
Nothing is stored. The page has no back end to send data to, and holds your input only in memory.
Nothing at all. There is no registration, no paywall and no per-use quota.
The logic is straightforward and testable; the worked example above uses the tool’s own defaults so you can verify it yourself.