The part that is 3% lighter is the worse part. Design with what you can buy

Every engineer has been taught that the best part is the one with the best numbers. Lightest, strongest, lowest noise, highest efficiency. Choose on the datasheet, and let purchasing sort out the rest.

Here is the claim: a part that is 3 percent lighter, but has a 16-week lead time or a "not recommended for new designs" flag, is a worse part. Not a slightly worse part on balance. A worse part, because a design you cannot build on time is not a design, it is a drawing.

Supply-aware design is the habit of checking availability and price while you are choosing, not after. It sounds obvious. Almost nobody does it, because until recently it was too slow to do at design time.

Why the check happens too late

The usual loop is: design, release, purchase, discover. The engineer picks parts in the EDA tool or the CAD assembly, the BOM goes to whoever orders, and the problems come back a week later as a list of substitutions. Some of those substitutions are trivial. Some change a footprint, a mounting pattern, a firmware driver, or a thermal budget, and the design goes around the loop again.

The reason the check is late is cost. Opening a distributor's site for every candidate, for every part, for every revision, is hours of clicking. Engineers batch it to the end because batching is the only way it fits. The parts that get skipped are the ones where the datasheet looked great.

What the late check costs

Three kinds of damage, in rising order.

Rework. A connector that is out of stock gets replaced by one with a different pin pitch. New footprint, new board spin, new fab run.

Schedule. A microcontroller with a long lead time means a prototype that ships when the part ships, not when the design is done. The team works around it with dev boards, and the dev board is a different part with different behavior.

Lock-in. A part marked NRND still ships today. In eighteen months it does not, and the design has to be re-qualified with a replacement that was available all along.

None of these show up in the datasheet. They show up in the calendar.

Standard parts are not automatically safe

The instinct is to say: use standard parts and the problem goes away. It helps. It does not go away, because "standard" hides more variation than it suggests. Four examples.

M3 heat-set inserts. The thread is standard. The outside is not. Inserts for the same M3 thread come in different lengths and outside diameters from different makers, and each wants a slightly different hole in the plastic. A printed enclosure designed around one vendor's insert may not grip, or may crack the boss, with another's. If you check which insert is actually in stock before you set the hole diameter, the enclosure is right the first time.

NEMA 17 stepper motors. NEMA 17 fixes the faceplate size and the mounting hole pattern. It says nothing about the shaft length, the shaft flat, the rated current, the holding torque, the connector, or the body length. "Any NEMA 17" turns into "this NEMA 17" the moment you draw the bracket and the coupler. If the one you drew around has a long lead time, the alternates that bolt on are the ones with the same body length and shaft; a parts search that ranks by compatibility finds those, a search by name does not.

TMC2209 stepper drivers. The chip is one part number, but most projects use it on a plug-in driver module, and those modules come from many makers with different pin orders, different sense resistors, and different top-side versus bottom-side layouts. A design that assumes one module's pinout is a design that assumes that module is in stock.

ESP32-S3 modules. The ESP32-S3 is a family. The module variants differ in antenna (PCB or external connector), flash size and PSRAM, and those differences are baked into the part number suffix and into your firmware and your board outline. Pick the suffix with the right memory and then find out it is the one with no stock, and you are choosing between a board change and a firmware change.

In every case the datasheet choice was fine. The supply choice was never made, so it was made for you.

What changes when the assistant has a parts tool

An AI assistant with a parts search tool makes the supply check cheap enough to do inline, in the middle of a design conversation. Three things become normal.

Search by specification, at design time. Instead of "find a 3.3 V LDO" and a tab full of results, the assistant asks the tool for a 3.3 V LDO with a given dropout, package and current, in stock, and reports back with the candidates and their prices while you are still deciding the power tree. The choice is made with supply in view.

Alternates ranked by compatibility. When a part is flagged, the question is not "what else exists" but "what else fits." Same package, same pinout, same key limits, and only then "what does it cost and when does it ship." A tool that ranks alternates by compatibility turns an afternoon of datasheet comparison into a short list you review.

Stock checked at every revision, not at release. Because the check is one tool call, it can run every time the BOM changes. The agent scans the project, resolves every line, and tells you which lines moved: a part went out of stock, a price break shifted, a module variant was discontinued. You see it in the commit, not in the purchasing email.

The engineering judgment stays with you. The tool does not know whether the lighter bracket matters for this product or whether a long lead time is fine for a ten-unit batch. It gives you the numbers early enough to decide.

How to set this up with Claude Code, including the repo layout and the review loop, is in how to use Claude Code for hardware design. What a parts tool over MCP looks like from the assistant's side is in MCP in five minutes.

A simple rule for the design review

Add one column to the part selection table: can we buy it, at this quantity, this month, at a price we accept. A design criterion next to weight and tolerance, not a purchasing step.

Criterion	Where it comes from	When to check
Electrical or mechanical fit	Datasheet, drawing	While choosing
Weight, size, performance	Datasheet, your model	While choosing
Lifecycle status (active, NRND, obsolete)	Supplier data	While choosing
Stock at your quantity	Live search	While choosing, and at every BOM change
Landed price and lead time	Live quote	While choosing, and before release

The last three rows used to live in a different department. They decide whether the first two rows ever become a product.

The Next Everything way

This is the idea the product is built around. Next Everything connects to your assistant as an MCP server and gives it the tools to make the supply check part of design: nx_search_parts for live stock, price and compatibility-ranked alternates by MPN, spec or plain description; nx_scan_project to resolve a whole KiCad, CadQuery or firmware project to orderable parts and flag the ambiguous lines; nx_quote and nx_quote_fabrication for landed prices on electronics, PCBs, 3D prints and CNC parts. When you are ready, nx_checkout produces a payment link you open yourself; the assistant cannot spend money.

Out-of-stock parts come back with a clearly marked matching replacement and nothing is swapped without your OK. MOQ and price breaks are shown before you pay. The service is free; you pay only for the parts in an order you approve, at the price shown.

The check takes a prompt. Make it before the bracket is drawn, not after.

Sign up, paste one snippet into your assistant, and the next time you pick a part, ask whether you can buy it. The docs have the details, and the step-by-step for a KiCad project is in order parts for a KiCad project from Claude Code.