How to use SpeakCAD in ChatGPT: design a printable part in the chat

What SpeakCAD adds to ChatGPT

On its own, ChatGPT can describe a part or write OpenSCAD code, and you still need a CAD tool to check it, a fix when the mesh comes out broken, and a slicer. With SpeakCAD connected, ChatGPT keeps the part it is good at, the conversation: what the part holds, how it mounts, which measurements matter, which printer you have. Then it hands the description to SpeakCAD, whose own CAD AI builds a dimensioned model with the FDM design rules applied (walls a nozzle can print, clearance on the fits, a flat base on the bed) and exports a watertight file. It is the same AI and the same rules as in the SpeakCAD editor, and the part is saved in your SpeakCAD models like any other.

With SpeakCAD, ChatGPT can:

• Design a part from a description with its measurements, in about one to two minutes.
• Change it in words, one change at a time, each change a new version; earlier versions are kept.
• Read where it stands: its size, its named dimensions and SpeakCAD's note on the last change.
• Give you the file: an STL or 3MF download link, or G-code sliced for your printer among 380+ printers.
• Find a ready-made part in the SpeakCAD library and the maker marketplace.
• Check your balance and what things cost, so it quotes the right price.

Before you start

• A SpeakCAD account. Sign up on speakcad.com; it asks for no card. Designing, changing and downloading parts spend credits exactly as on the site, so add Starter credits ($5, once) or a plan before the first part. You can also create the account from ChatGPT's sign-in window.
• ChatGPT in a browser for the setup. Plugins are added in ChatGPT's settings on chatgpt.com. Once SpeakCAD is connected, you use it in your chats.
• For developer mode, a paid ChatGPT plan. OpenAI offers developer mode on Plus, Pro, Business, Enterprise and Edu, on the web. In a Business, Enterprise or Edu workspace, an admin decides whether developer mode and outside plugins are allowed.

Add SpeakCAD from the plugin directory

1. On chatgpt.com, open Settings, then Plugins (some accounts still call the page Apps & Connectors).
2. Search for SpeakCAD and open it. Check that the developer is SpeakCAD and the website speakcad.com.
3. Press Connect, then sign in as described below.

If SpeakCAD does not come up for you, add it in developer mode. It is the same server and the same result.

Add SpeakCAD in developer mode

Developer mode lets ChatGPT use a plugin by the address of its server. ChatGPT warns that such plugins are not reviewed by OpenAI; the address below is SpeakCAD's own, on speakcad.com.

1. On chatgpt.com, open Settings, then Security and login, and turn on Developer mode. On older versions of ChatGPT the switch is on the Apps & Connectors page, under Advanced settings.
2. Open Plugins in the settings and press + (on older versions, Create on the Apps & Connectors page).
3. Name: SpeakCAD. Description, if asked: Design 3D printable parts by chat.
4. Server URL: https://speakcad.com/api/mcp
5. Authentication: OAuth. Leave the client ID and secret empty: SpeakCAD registers ChatGPT by itself.
6. Press Create, then sign in.

Sign in and allow ChatGPT

ChatGPT opens a SpeakCAD window. Sign in the way you usually do (e-mail and password, Google, or a sign-in link by e-mail), or create the account there. The next page names the assistant asking for access, ChatGPT, and the address it will send you back to. Press Allow if you started the connection yourself.

From then on ChatGPT can design, change, download and slice parts in your SpeakCAD account, paid with its credits, the same way you would on the site. It never sees your password.

Your first part

Start a new chat and pick SpeakCAD: type @SpeakCAD, or open the + menu and choose SpeakCAD (under Developer mode if you added it there). Then say what you need, with the measurements:

If you do not have every number yet, let ChatGPT ask first: "I need a wall mount for my router. Ask me what you need to know, then design it with SpeakCAD." The questions it asks (the router's size, where the cables go, how it hangs) are what makes the first version right.

Good requests share three things: measurements in millimetres, what the part fits or holds, and how it attaches. How to describe a part has templates for brackets, enclosures, knobs and stands.

In the SpeakCAD card

While SpeakCAD designs the part, ChatGPT shows the SpeakCAD card with "SpeakCAD is designing your part…". One to two minutes later the part appears in 3D, with its size and its version number. Around it:

• The part's named dimensions (wall thickness, width, hole diameter…) as number fields. Type new values and press Apply the dimensions: no AI and no credits, saved as a new version.
• A change in words: type "walls 3 mm" or "a 5 mm hole in the lid" and press Change it. SpeakCAD's AI makes the change (2 credits, included in Unlimited) and the card shows the new version.
• STL and 3MF: a download link, valid 24 hours.
• G-code for your printer, with Adjust the printer or settings to choose the printer, the nozzle, the print profile, the material, infill, walls, supports, adhesion and speed.
• Open in SpeakCAD editor: the same part in the full editor.

ChatGPT is told what happens in the card, so the conversation carries on: "the phone slot is 2 mm too narrow" works in the chat as well as in the card. If your version of ChatGPT shows no card, ChatGPT still gets the part's size, its dimensions and the links, and gives them to you in its reply.

Changes that work

One change per message works better than five: SpeakCAD changes what you asked for and keeps the rest. Give the amount ("2 mm wider", "walls 3 mm") rather than an adjective ("bigger", "sturdier"). When the number you want to change is already in the card, typing it is quicker and free.

For changes where you need to point at something (this face, that hole), open the part in the editor: you click the face and describe the change, every version is kept and can be restored, and Fit Check prints a five-minute test piece that calibrates the clearances to your printer.

G-code for your printer

Say which printer you have and how you want to print: "slice it for my Bambu Lab A1 in PETG, 0.2 mm layers, 30% infill". ChatGPT looks the printer up among 380+ printers from 60+ brands and checks your settings against its OrcaSlicer profile: a layer height the profile does not have is refused, with the ones it has. The card then opens the slicer on the part with everything selected. Press the G-code button and the file comes back as a download link, a .gcode file or a sliced .gcode.3mf for Bambu Lab printers, with the print time, the filament in grams and the layer count. G-code counts as a download, plus 5 credits for the slice (included in Pro and Unlimited).

Tell ChatGPT your printer once. With ChatGPT's memory on, say "remember that my printer is a Bambu Lab A1 with a 0.4 mm nozzle and I print PLA and PETG", and later slices start from it.

A file you already have

The card slices your own STL or 3MF too. Ask "slice my STL for my Prusa MK4S in PLA" and drop the file on the card when it opens. It goes from your browser straight to the slicer service and is deleted when the job ends; ChatGPT never receives it and only learns the print time, the filament weight and the download link. Slicing your own file follows the online slicer's price: The online slicer gives every account 1 free slice, its first (a free account, no card). After that, a slice uses one slice from a Slicer pack (20 slices for $3, once, never expire) or 5 credits, and slicing is included in Pro and Unlimited. Re-slicing the same file with other settings within 10 minutes is free.

If G-code is all you ever need, the separate SpeakCAD Slicer plugin, at https://speakcad.com/api/mcp/slicer, needs no sign-in: see slice from ChatGPT or Claude.

On your phone

The ChatGPT app for iPhone and Android uses the plugins connected to your ChatGPT account, so SpeakCAD from the directory is there once you have connected it. Developer mode is a web feature, and whether a plugin added in developer mode also shows in the app depends on the ChatGPT version. When it does not, open chatgpt.com in the phone's browser.

Every part designed from ChatGPT is also in your SpeakCAD models, and the SpeakCAD editor runs in Safari and Chrome on a phone, with the same 3D view, dimensions and downloads.

What it costs

Exactly what it costs on the site, from the same balance: 2 credits per AI request (the first design or a change), 10 credits per download (a paid design re-downloads free after small fixes), and 5 more for G-code (included in Pro and Unlimited). Unlimited also includes the requests and downloads. Typing new dimensions, turning the part around in 3D and asking ChatGPT questions spend no credits. Connecting SpeakCAD to ChatGPT is free; developer mode needs a paid ChatGPT plan, which is OpenAI's, not SpeakCAD's. Ask "how many SpeakCAD credits do I have left?" at any time.

What ChatGPT and SpeakCAD see

• ChatGPT sends SpeakCAD the description of the part, each change you ask for, and the printer and settings for a slice. SpeakCAD does not see the rest of the conversation.
• SpeakCAD sends back the part's status, size, dimensions, version and links. Files come as download links, never pasted into the chat.
• Files you drop on the card go from your browser to SpeakCAD's slicer, never through ChatGPT.
• The privacy policy has a section on assistant connectors.

To disconnect, open the Plan page of your SpeakCAD account: Connected assistants lists ChatGPT with a Disconnect button that cuts it off at once. You can also remove SpeakCAD in ChatGPT's Plugins settings.

When something goes wrong

• SpeakCAD is not in the + menu. Start a new chat and check that SpeakCAD shows as connected in Settings, Plugins. A plugin added in developer mode is listed under Developer mode in the + menu, and developer mode has to stay on.
• ChatGPT writes the part itself instead of calling SpeakCAD. Say "use SpeakCAD to design it", or pick SpeakCAD for the message as above.
• ChatGPT asks you to confirm first. ChatGPT can ask before a plugin designs, changes or downloads something. Confirm to go ahead; if you decline, nothing is spent.
• The sign-in window closed and nothing connected. Allow pop-ups for chatgpt.com and press Connect again.
• Not enough credits. The card's Add credits button opens your SpeakCAD Plan page.
• The design takes more than two minutes. It finishes anyway and lands in your SpeakCAD models. Ask ChatGPT "is my part ready?", or open it in the editor.

No plugin? Paste the description

The plugin is a convenience. On any ChatGPT plan, the free one included, ask ChatGPT to write the part down with every measurement, copy the text and paste it into SpeakCAD: the numbers are used exactly. The ChatGPT to STL page shows what to keep from the conversation.

Using Claude instead? SpeakCAD in Claude covers the same connector there, on the web, the desktop app and the phone.