Theme Migration Guard
Keep saved themes working when the tokens underneath them are renamed or replaced.
What it adds
A versioned migration path that upgrades stored themes as the token set changes beneath them.
What your agent is told to do
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What your agent is told to do
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Stamp every stored theme with the version of the token set it was written against, and refuse to apply a theme whose version you do not recognise rather than applying it partially.
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Write each token change as an explicit forward migration step — a rename, a split of one token into two, a merge, or a removal — and run the steps in order. Inferring the mapping by matching names produces plausible and wrong results the first time a token is split.
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Keep a record of which values a user actually chose and which were inherited from defaults, so a migration can carry the deliberate overrides forward and let everything else be regenerated from the current defaults.
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Supply a value for every token that becomes required, derived from the theme's existing values where a sensible derivation exists and from the shipped default where it does not. A theme missing a required token must never reach the renderer.
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Do not migrate lazily on read without persisting the result. A theme that is re-migrated on every load will be migrated twice by two tabs, will hide the cost of a slow migration, and will keep failing in exactly the same way with no record of it having failed before.
Edge cases it handles
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Edge cases it handles
7- Every saved theme needs a version stamp, because a theme with an unknown provenance cannot be migrated safely and must be refused rather than half-applied.
- User overrides have to survive the migration intact and distinguishable from inherited defaults, or a migration quietly resets the one colour somebody cared enough to change.
- Tokens that become required need a supplied value — derived where a derivation makes sense, defaulted where it does not — so no theme ever reaches the renderer incomplete.
- A migration interrupted midway must be recoverable. Write the result atomically, or keep the original alongside the new one until the migration is confirmed complete, so a failed upgrade does not leave a theme that is half old and half new.
- Two tabs or two devices may attempt the same migration at once; make the operation idempotent so running it twice produces the same theme as running it once.
- A theme created by a newer version of the app than the one running must be refused with a clear message rather than downgraded by guesswork.
- Keep the previous version of a migrated theme long enough for someone to revert, since a bad migration is usually only noticed after the user has closed the tab.
Definition of done
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Definition of done
9- Every stored theme carries the token-set version it was written against.
- Migrations are explicit ordered steps, not name matching.
- User-chosen values are preserved through migration and remain distinguishable from defaults.
- Newly required tokens receive derived or default values, and no incomplete theme reaches the renderer.
- An interrupted migration leaves either the original theme or the fully migrated one, never a mixture.
- Running a migration twice produces the same result as running it once.
- A theme from a newer version is refused with a clear message.
- The feature matches the existing design system.
- No existing functionality is broken.
Related features
Z-Index Registry
Z-Index Registry
Keep every stacking value in one file so nobody has to guess a bigger number.
What it does
A single source of named z-index tokens, with reserved ranges per layer and a check that blocks raw values.
How it works
- 1 Find every z-index in the codebase, including inline styles and values buried in third-party overrides, and list them with the component that owns each. The count is usually higher than anyone expects and several will be arbitrary large numbers.
- 2 Reserve a range for each layer rather than assigning single values, so a new dropdown can slot between existing ones without renumbering everything above it. Leave real gaps between ranges.
- 3 Name each token after the layer it belongs to and derive the ordering from Elevation Layer Map. That feature decides what covers what; this one holds the numbers and stops them being invented locally.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/z-index-registry
Spacing Scale
Spacing Scale
Reduce the app's spacing to a small set of steps that repeat across every surface.
What it does
A named spacing scale covering gaps, padding, and section rhythm, with every existing value in the app mapped onto it.
How it works
- 1 Collect every spacing value currently in the codebase and count how often each appears. The result is usually a handful of genuine intentions surrounded by dozens of near-misses that were nudged once and never revisited.
- 2 Define a scale that is fine at the small end, where control padding lives, and coarse at the large end, where section separation lives. A linear scale gives too many indistinguishable large steps and too few small ones.
- 3 Separate the tokens used inside a component from the ones used between components and between page sections, and name them so the difference is obvious. The same number serving both purposes means a change to button padding also changes the gap between sections.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/spacing-scale
Shadow Scale
Shadow Scale
Replace ad hoc shadows with a small set tied to what each surface actually is.
What it does
A fixed ladder of shadow tokens, each named for an elevation role rather than a blur radius.
How it works
- 1 Collect every shadow currently declared anywhere in the app and group them by what they sit on — a resting card, a hovered card, a dropdown, a dialog, a toast. Most apps have a dozen near-identical values that collapse into four or five roles.
- 2 Name each step for its role, not its appearance. A token called menu tells the next person which surfaces may use it; a token called shadow-md-2 does not.
- 3 Use a single light source for the whole scale, so offset, blur, and spread grow together as elevation rises. Two shadows lit from different directions on the same screen read as a rendering bug.
Copy the prompt
No account needed
Add this feature to my app:
https://addthisfeature.com/x/shadow-scale
How it works
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1
Copy the link
Grab the Markdown instruction URL for this feature.
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Give it to your AI
Paste it into Claude Code, Cursor, v0, Lovable — whatever you build with.
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It inspects, then implements
Your agent reads your existing app first, then adds the feature to fit it.
Works with your stack
These instructions are written to adapt. They tell the agent to detect your framework, match your existing design system, and reuse what you already have — rather than assuming a particular stack.
Need it tighter than that? Customize the feature and tell it exactly what you're running.