Tools
SMILES validator
Check whether a SMILES string is valid, get the canonical form and molecular formula, and see the structure — locally, no login.
Result
Status:Valid SMILES
- Molecular formula
- C9H8O4
- Canonical SMILES
CC(Oc1ccccc1C(O)=O)=O
Paste a SMILES string and this tool confirms whether it parses to a real molecule. When it does, you get the canonical SMILES (a single, normalized form so two strings for the same molecule match) plus the molecular formula and a 2D depiction. Invalid input is reported clearly rather than silently corrected. Everything runs in your browser.
How to validate a SMILES string
- 1.Paste the SMILES string you want to check into the input box.
- 2.If it is valid, the tool draws the structure and shows a "Valid SMILES" status.
- 3.Copy the canonical SMILES to store a normalized form that matches across equivalent strings.
- 4.If it is invalid, the tool flags it so you can fix the syntax before using it downstream.
Frequently asked questions
- What makes a SMILES string invalid?
- Common causes are unbalanced ring-closure digits, mismatched parentheses, unknown element symbols, or impossible valences. A validator parses the string the way chemistry software does and rejects anything that cannot describe a real molecule.
- What is a canonical SMILES?
- A canonical SMILES is a single, normalized representation of a molecule. Because one molecule can be written as many different SMILES strings, canonicalization produces one consistent string so equivalent molecules can be compared and de-duplicated.
- Is my SMILES uploaded anywhere?
- No. Validation and canonicalization run entirely in your browser with openchemlib. The string is never sent to a server.