SQL Query Optimizer
Find the patterns that stop a query using its indexes.
- Free
- No signup
- Nothing uploaded
- No watermark
Read in your browser. Your query is never sent anywhere, and no database is contacted.
How to Use the SQL Query Optimizer Online
Finds the patterns that stop a query using its indexes — a function wrapped around an indexed column, a leading wildcard in LIKE, an implicit type cast, or a missing leading column of a composite index. These defeat B-tree indexes in every major database, which is why the advice is portable.
No software to install Free Works on any device
Step-by-Step Guide to Using the SQL Query Optimizer
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1. Paste your SQL into the box — or press the example button to see what it expects
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2. Adjust the options underneath if the defaults do not suit you
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3. Copy the result, or download it as a file
Nothing is uploaded either way.
No .txt file to hand? Download a sample text and Markdown file (703 B) and try it.
What is the SQL Query Optimizer?
Finds the patterns that stop a query using its indexes — a function wrapped around an indexed column, a leading wildcard in LIKE, an implicit type cast, or a missing leading column of a composite index. These defeat B-tree indexes in every major database, which is why the advice is portable.
SQL files
.SQL .TXTFind the patterns that stop a query using its indexes.
Why Use SQL Tools Online?
Queries copied from logs, written in a hurry or moved between MySQL and PostgreSQL are hard to read and easy to break. These tools format, build, convert and check SQL in the page, so your schema and data stay with you.
“A well-formatted query is half debugged.”
- Readable queries at a glance
- INSERTs from CSV or Excel
- Syntax errors caught early
- Risky patterns flagged
- Dialects converted between databases
- JOINs and WHEREs built visually
- Test data generated
- Schemas kept off other servers
Popular Uses for Query Formatters
These cover the SQL chores that come up during development and reporting.
- Formatting a long query Turn a one-line query from a log into indented SQL you can read.
- Changing databases Convert MySQL table definitions to PostgreSQL or SQLite when moving a project.
- Loading spreadsheet data Turn a CSV or Excel sheet into INSERT statements for a quick import.
- Sample data Generate realistic test rows to try out a new table or report.
- Building joins Put together a JOIN between two tables without looking up the syntax.
- Syntax checks Catch a missing comma or bracket before running a query on the server.
- Security review Spot patterns that may allow SQL injection in queries built from user input.
- Query results as JSON Convert SQL rows into JSON or CSV for an app, report or spreadsheet.
What You Can Do with the SQL Query Optimizer
Accepts SQL, TXT
Understands SQL structure rather than treating the file as bytes
Reads the query plan rather than guessing from the text of the statement
Points at the specific clause responsible for the cost
Why Use ToolXkit for SQL Query Optimizer?
Your files stay with you
Everything runs inside your browser. Nothing you open or type is uploaded to a server.
Free, with no catch
No signup, no watermark and no daily limit on how often you use it.
Fast
Results appear in seconds, because nothing has to travel over the internet and back.
Works on any device
Use it on a computer, tablet or phone, in Chrome, Edge, Firefox or Safari.
Nothing to install
No app, no extension and no desktop program. Open the page and start.
Made for real people
Plain words and clear buttons, built by one developer who wanted tools like this to exist.
Database Tools for Different Users
Backend developers
Format, check and convert queries while building features and fixing bugs.
Database administrators
Move schemas between dialects and generate index and ALTER statements.
Data analysts
Load CSV files as INSERTs and tidy long reporting queries for sharing.
SQL learners
See how SELECT, JOIN and WHERE clauses fit together by building them step by step.
QA engineers
Fill test databases with fake rows and check queries used in tests.
Report writers
Get queries explained in plain words before changing a report someone else wrote.
Best Times to Format or Convert SQL
SQL tools help when you are:
- Reading a query from a log
- Switching from MySQL to PostgreSQL
- Importing a spreadsheet into a table
- Seeding a test database
- Reviewing a colleague’s pull request
- Learning SQL for the first time
- Hunting a slow report query
- Checking code for injection risks
Frequently Asked Questions
Answers to common questions about this tool.
Does this work for PostgreSQL and MySQL queries?
Yes — the patterns it flags are ones both engines share, because they come from how B-tree indexes work rather than from any one database. A function wrapped around an indexed column, a leading wildcard in LIKE, or an implicit type cast defeats the index in PostgreSQL, MySQL, SQL Server and SQLite alike.
What exactly stops a query using its index?
Most commonly: applying a function to the indexed column (WHERE YEAR(created) = 2026 rather than a date range), a LIKE pattern beginning with %, OR across different columns, comparing a string column to a number, or a leading column of a composite index missing from the WHERE clause. Each is flagged with the rewrite.
Does it replace EXPLAIN?
No, and nothing can. EXPLAIN shows what your database actually decided, using statistics about your real data. This reads the SQL text and finds patterns that reliably cause trouble, which is useful before you have a slow query to explain — but always confirm with EXPLAIN against the real table.
Which SQL dialects does SQL Query Optimizer support?
Most SQL tools here handle the common dialects, including MySQL, PostgreSQL, SQLite and SQL Server. Where a dialect choice matters, pick the one that matches your database before copying the result.
Is it safe to paste production queries into SQL Query Optimizer?
As far as this site is concerned, yes. Queries are processed in your browser and are not uploaded or logged. Still avoid pasting real passwords or personal data anywhere you do not need to.
Does formatting change what my query does?
No. Formatting only changes spaces, line breaks and the letter case of keywords. The query returns the same results before and after, it is simply easier to read.
Will a converted schema work first time on the new database?
Common types and statements convert cleanly, but every database has its own features, such as special data types or functions. Review the output and test it on a copy before running it on live data.
Is SQL Query Optimizer free without an account?
Yes. Use it as often as you like with no sign-up and no paid tier. It works in any modern browser on a work or personal computer.
Further reading
- The SQL Language (PostgreSQL documentation) The PostgreSQL manual’s chapter on the SQL language and its commands.
- SQL As Understood By SQLite (sqlite.org) SQLite’s own reference for every statement it understands.
- SQL (Wikipedia) A readable overview of SQL, its history and how the standard relates to each database.
More SQL Tools
Other free tools for the same kind of job.
- ALTER TABLE Generator Build an ALTER TABLE to add, drop, rename or retype a column. Open tool
- CREATE TABLE Generator Build a CREATE TABLE statement column by column. Open tool
- CSV to SQL Converter Turn a CSV file into CREATE TABLE and INSERT statements. Open tool
- CSV to SQL INSERT Generator Turn CSV rows straight into INSERT statements. Open tool
- DELETE Query Generator Build a DELETE statement that will not empty the table by accident. Open tool
- Excel to SQL Converter Turn a spreadsheet into CREATE TABLE and INSERT statements. Open tool
- Fake SQL Data Generator Fill a table with realistic names, emails and dates from its CREATE TABLE. Open tool
- INSERT Query Generator Build an INSERT statement with values quoted correctly. Open tool
- JSON to SQL Converter Turn a JSON array into CREATE TABLE and INSERT statements. Open tool