Placeholder

Skill MauricioPerera/llms-txt-skills/skills/placeholder

RFC v0.8 + implementación de referencia para publicar Agent Skills a través de llms.txt. Incluye parser, validador, schema JSON y skills de ejemplo.

Install

npx -y skills add MauricioPerera/llms-txt-skills --skill placeholder

Assembled from the repository path, not quoted from the project. Check it against their README if it does not work.

One thing to look at

2 stars2 stars. Stars are a popularity signal and not a quality one, but at this level it is likely that nobody has read this closely except its author, and you would be relying on your own review.

What its author says it does

Copied from the file, not written here

Generate SVG placeholder images for UI mockups via the placeholder-img HTTP API. Use when the user asks for placeholder images, mockup assets, or dummy images with specific dimensions and colors.

The file declares its own license as MIT. That is the author’s claim about this one file, and it is not the same thing as the license GitHub reports for the repository, which is listed with the other numbers below.

SKILL.md

3.1 KB, as published. Nobody here has run it

placeholder

Build URLs for the placeholder-img API to embed mockup images in HTML, CSS, or design prototypes.

When to use

User asks for a placeholder image of size W×H.
User is prototyping a UI and needs a dummy <img> source.
User wants a colored block of a known aspect ratio as a background.

Do NOT use this skill for production images, photography, or when the user wants real content — this generates blank colored SVGs with the dimensions drawn as text.

When to prefer this over alternatives

Over CSS color blocks (<div style="background:#ccc;width:400px;height:300px">): when the mockup needs to behave like a real image — responsive aspect ratio, <img> semantics for alt text and lazy-loading, usable as <img srcset> or background-image interchangeably.
Over third-party services like placehold.co or via.placeholder.com: when the user wants a self-hosted source with no third-party dependency, guaranteed immutable cache (max-age=31536000, immutable), and a stable domain they control.
Over inline data:image/svg+xml URIs: when the mockup is referenced from more than one place, when HTML readability matters, or when the dimensions are dynamic and embedding SVG string-templates would clutter the code.

If none of the above apply — e.g., the user is already using a design system with built-in skeleton components, or a CSS block is genuinely sufficient — prefer the simpler option and do not call this API.

Base URL

https://img.automators.work

Build the URL

{base}/{width}x{height}[?bg={hex6}]

width, height: integers in px, each ≤ 4000.
bg (optional): 6-digit hex without #. Defaults to cccccc. Invalid values silently fall back to the default.

Examples

Intent	URL
Generic 400×300 placeholder	`https://img.automators.work/400x300`
Dark-blue banner	`https://img.automators.work/1200x400?bg=1e3a5f`
Square brand tile	`https://img.automators.work/512x512?bg=f97316`

Output the agent should produce

When the user asks for a placeholder in HTML context, emit:

<img src="https://img.automators.work/{W}x{H}{?bg}" alt="{W}×{H} placeholder" width="{W}" height="{H}">

When the user asks for a CSS background:

background-image: url("https://img.automators.work/{W}x{H}{?bg}");

Constraints

Stateless, no auth, no rate limit beyond Cloudflare's platform default.
Responses are immutable and cached one year — the same URL always yields the same SVG.
There are no endpoints other than /{W}x{H}. Do not invent paths.

Failure modes

If width or height is not an integer, the API returns HTTP 400. Re-prompt the user for valid dimensions.
If bg is not a 6-digit hex, the SVG is still returned but with the default gray background. Warn the user if they asked for a specific color.