Extract a Substring
Grab a fragment of a string by start position and length. Runs entirely in your browser, so your data never leaves your device.
0 chars · 0 lines
Output
The result appears here as you type.
How to use Extract a Substring
- 1. Paste the source string. Enter the string you want to grab a fragment from into the input pane, from a short code to a longer line of text.
- 2. Set start position and length. Enter the zero-based Start position where the fragment begins, and the Length in characters to take from that point onward.
- 3. Copy the extracted substring. Copy the resulting fragment and use it wherever you need just that portion of the original string, such as a specific field from a fixed-format record.
When to use Extract a Substring
Extract a Substring grabs a fragment of a string by start position and length, the same operation a substr or slice function performs in code. It answers 'what characters are at this exact position' without writing any code.
- Pulling a field from a fixed-width record. A legacy data file stores each field at a fixed character position, and extracting the substring at the known offset and length gives you just that field's value.
- Checking what a slice expression would return. You are debugging code that uses substring or slice logic and want to manually verify what characters a specific start index and length would extract from sample data.
- Trimming a known prefix or suffix by position. You know exactly how many characters to skip at the start of a string, like a fixed-length ID prefix, and want to extract just the meaningful part that follows.
- Sampling a portion of a long string for review. You have a very long string, like a hash or token, and want to check just a middle section of it without scrolling through the entire value.
Examples
Characters 0–5
Input
abcdefghij
Output
abcde
About the Extract a Substring tool
Extract a Substring is a free online tool that works entirely inside your web browser. Grab a fragment of a string by start position and length. Because the processing happens on your own device, nothing you enter is uploaded, logged or stored anywhere.
This page is one of 159 String utilities on EditSafely. Each one does a single job well, and all of them follow the same rule: your input stays on your machine.
You can shape the output with 2 settings, including Start position (0-based) and Length (characters), and the result refreshes the moment you change one. A worked example further down the page shows exactly what the tool produces for a real input.
Because nothing leaves your device, the tool is suitable for sensitive content such as internal documents, credentials or customer data. It also responds instantly, since every keystroke is handled on your own machine rather than by a remote API.
Frequently asked questions
Does Extract a Substring cost anything?
Yes, it is completely free. All 2,658 tools on EditSafely work without an account, a subscription or usage limits.
Is it safe to paste sensitive or confidential data?
No data leaves your device. The whole tool is JavaScript that runs inside your browser tab, so there is no upload, no server-side processing and no log of what you did. If you disconnect from the internet after the page loads, it keeps working.
How much text can I process at once?
There is no fixed limit. Because the work happens on your own device rather than on a shared server, the practical ceiling is your machine's memory, which comfortably handles inputs far larger than typical online tools allow.
Do I need to sign up or install anything?
Nothing to install and no account needed. Open the page in any up-to-date browser, including on a phone or tablet, and the tool is ready.
How do I use the result?
The output panel has a one-click copy button, and you can keep refining the input while you work; the result updates in place as you type.