Evaluating Image Placeholder Generators, Feishu Integration Issues, and a Custom Solution

For frontend developers, an image placeholder generator is an essential tool when product images are unavailable or when testing responsive layouts with various image sizes.

The author describes common scenarios: completed page layouts awaiting images from designers, and the time‑consuming process of searching, downloading, and resizing images, which also raises copyright concerns.

A recent requirement involved adding a small feature to a Feishu shortcut, demanding custom width, height, text, colors, format (PNG), font size, and Feishu compatibility.

Initial research listed ten online placeholder services (e.g., Placeholder.com, Lorem Picsum, Dummy Image) with their URLs, usage examples, and features, noting that only a few roughly met the needs but lacked Chinese language support.

Further searching uncovered additional services such as placehold.co, fakeimg.pl, tool.lu, and devtool.tech, each with example URLs; however, fakeimg.pl and tool.lu failed when used as attachments in Feishu, and devtool.tech only produced SVG output.

Because none of the existing services satisfied all requirements, the author decided to implement a custom solution.

Using AI assistance, the author wrote the code in about half an hour, deployed it locally without issues, but encountered the same Feishu error upon deployment.

execute error，捷径执行出错：
Error: execute原始执行结果：
捷径返回错误码： FieldCode.Success 
 转换结果：transform cell value fail

Investigation revealed differences in response headers: the presence of Access-Control-Allow-Origin and the Content-Length header, with the latter being the root cause of the Feishu failure.

The author concludes that Feishu likely has a bug in handling images without a proper Content-Length header.

A free, self‑hosted placeholder service was deployed at https://www.kaifage.com/tools/placeholder , providing the needed functionality.