Troubleshooting

Every error GDN raises names the file, line, and column, and often adds a plain-English hint:

error: Object of type `dict` has no attribute `status_code` (app.star:12:8)
  (hint: a dict is read with ["status_code"], not .status_code; http.get returns a dict)

You'll see these in the Studio message console, in the live preview, and from gdn check apps/<id>. This page maps the common ones to the fix.

Errors in your code (app.star)

These stop the render. The message is the part after error:.

The message says	What it means	Fix
cannot use reserved keyword import	Starlark has no imports or libraries	Delete the import. Everything is handed to you as c, ctx, http, math, fmt. See Starlark vs Python.
cannot use reserved keyword while	There are no while loops	Use for i in range(n):.
cannot use reserved keyword try	Starlark has no exceptions	Guard with if instead — check status_code, check for None.
Variable datetime not found (or random, os, time…)	You reached for a Python module that doesn't exist	Use the built-ins: ctx.now for time, the math struct for math.
Object of type dict has no attribute status_code	You wrote resp.status_code on an http.get result	It's a dict: resp["status_code"]. Same for ctx.inputs — use ctx.inputs["key"] or .get("key"). See HTTP.
Operation + not supported for types string and int	You joined text and a number	Wrap the number: "N" + str(n).
Index N is out of bound	You indexed past the end of a list	Check len(...) first, or guard the index.
Floor division by zero	A // or % had a zero on the right	Guard the denominator before dividing.
unknown font '9x9'	That font name isn't bundled	Use a real one ("5x7", "8x12", …); run gdn fonts to list them, or see Fonts.
bad color 'purpel'	Misspelled or unknown color	Use a valid name, a hex like "#ff8800", or an (r, g, b) tuple. See Colors.
op limit (4096) exceeded on a single page	One page issued too many draw calls	Draw less per page, or split across pages. See Limits.
render timed out (>30s)	The render ran too long — usually a runaway loop	Remove the infinite loop; keep for ranges bounded. See Limits.

Validation warnings and errors (gdn check / Validate)

These come from checking the app as a whole, not from running your code. Errors block publishing; warnings don't, but most are worth fixing.

The message says	What it means	Fix
page X has no matching def X(c, ctx)	The manifest lists a page your code doesn't draw	Add def X(c, ctx): in app.star, or remove X from pages:.
setting k is declared but never used in app.star	A manifest input your code never reads	Read it with ctx.inputs.get("k", ...), or delete it from the manifest. In Studio, the Use it in my code button does this for you.
draws x.png but it's not listed under assets:	You drew an image you didn't declare	Add the filename under assets: in the manifest. See Working with images.
text "..." has lowercase; fonts are UPPERCASE-only	Lowercase text draws nothing	.upper() the string.
input key k must be letters and digits only	An input name has _, -, or a bad first character	Rename it (tzoffset, not tz_offset). Required for api-key inputs. See Inputs.
width must be 1-384	Panel too wide	Pick 64, 128, 192, up to 384. Height is always 32.
refresh Ns is very fast	Refresh under ~60s	Raise it — 60+ is easier on data sources. See Limits.
unknown manifest key	A typo'd or unsupported manifest field	Check the spelling against the manifest reference.

It runs but looks wrong

No error, but the panel isn't what you expected.

Symptom	Likely cause	Fix
Text is invisible	Lowercase (fonts are uppercase-only), drawn off the 32px-tall canvas, or the same color as the background	.upper() it; check x/y are on-panel; use a contrasting color
Only part of the text shows	It's wider than the panel	Use a smaller font, c.text_wrapped, or shorter text. See Text layout
Nothing draws at all	The page function never ran, or its name doesn't match pages:	Make sure the manifest's page name matches the def name exactly
The last frame won't clear	You didn't start with c.clear()	Begin each page with c.clear()
The clock/date is off by hours	ctx.now is UTC, not local	Convert with an offset or a time API — see Handling time
Live data never appears	The fetch failed and there's no fallback	Check resp["status_code"] != 200 and draw a fallback. See HTTP

Still stuck?

• Run gdn check apps/<id> for the full list of problems at once.
• In Studio, the Debug button (bottom-right) keeps a copyable log of failed requests.
• The live preview catches most of the "looks wrong" issues in seconds — including time travel for date-driven apps.