MCP server · Research
Molecules MCP server
by laszlopere
Your AI can compute molar masses, isotope patterns and look up compounds using trusted NIST chemistry data.
This is a small helper that gives your AI real chemistry tools. Instead of guessing what a molecule weighs, it looks the numbers up in official NIST data and does the math for you. It is handy for anyone who works with formulas, lab work, or study notes and wants answers they can trust.
What is an MCP server? The 30-second version
On its own, your AI can only chat and recall things from memory, which is not reliable for numbers. An MCP server is a small helper program that gives your AI a new skill or a connection to a service. This one connects your AI to trusted chemistry data from NIST, so it can compute molar masses and isotope patterns instead of guessing them. You just ask in normal words, and the AI uses this helper behind the scenes.
What this MCP server does
You ask your AI a chemistry question, like what a mole of glucose weighs. The AI passes the formula to this helper program. The helper parses the formula, looks up each element in bundled NIST data, and computes the answer. You get the result back in the chat, with the option to include uncertainty or per-element percentages. For names and formulas, it can also search a bundled compound database and, if allowed, look things up online.
Click to zoomWhat you can do with it
- Compute the molar mass of a chemical formula
- Show the percent composition by mass for each element
- Report molar mass with its uncertainty
- Compute the monoisotopic mass used in mass spectrometry
- Show the isotope pattern peaks for a formula
- Look up a compound by name or by formula
- Find isomers that share the same formula
Try asking your AI
- “What does a mole of glucose weigh?”
- “How much of Fe2(SO4)3's mass is iron?”
- “What's the molar mass of caffeine, with uncertainty?”
- “What does the mass spectrum of chloroform look like?”
- “Which compound has the formula C9H8O4?”
What it gives back to you
You get clear answers in the chat: a number with its unit, like g/mol, sometimes with a plus or minus uncertainty. For isotope patterns you get a list of peaks with their mass, m/z and relative intensity. For lookups you get compound names and formulas, with the preferred name first. It can also show a breakdown of each element's share of the mass.
Before you start
What you need
- Python and the uv tool installed on your computer
- The Claude desktop app or Claude Code
Good to know
Compound lookups can go online by default, so if you need to keep your queries private, turn that off with the MCP_MOLECULES_ONLINE setting.
Install it with your AI
Add Molecules MCP server to your AI, no technical skills needed
You don't install anything by hand. You copy one prompt, paste it into an AI that can work on your computer, and it checks, installs and connects the server for you, asking you when it needs something.
Sign in to get the install prompt
Members get a ready-made prompt that lets the Claude desktop app check Molecules MCP server, install it and connect it for them, step by step. You don't need any technical skills: you copy, paste and answer a few questions. Your connected AI can also find and install any of the 4,066 MCP servers here for you.
Who it's for
Students, teachers, lab workers, and anyone who needs quick, trustworthy chemistry numbers without doing the math by hand.
