LinkPreloadDetector

Extract preload link hints from HTML source without fetching, validating browser support, or resolving their hrefs.

Description

Preload links announce resources that a browser may fetch before ordinary discovery.

Preload links announce resources that a browser may fetch before ordinary discovery. Finding a hint does not prove that its destination or fetch settings are valid.^[1]

Extract preload link hints from HTML source without fetching, validating browser support, or resolving their hrefs.

When to use LinkPreloadDetector

Use this tool to extract preload link hints from HTML source without fetching, validating browser support, or resolving their hrefs.

Choose the URL, decoded source text, header value or explicit byte list requested by this tool. Paste the complete relevant input and follow its parsing and encoding conventions.

How to use LinkPreloadDetector and understand its results

Choose the URL, decoded source text, header value or explicit byte list requested by this tool. Paste the complete relevant input and follow its parsing and encoding conventions.
Enter html using the field table and calculation rules, then run the tool.
Read hrefs. The explanation below defines the units, signs, ordering and any flags or placeholder values.
If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.

Input field	Meaning	Value type; see rules below	Requirement
html	HTML source.	string; maximum length: 1000000	Required

Paste HTML. Scan link start tags and case-insensitive ASCII-whitespace rel tokens, collect matching href values and decode supported references. Preserve source order and duplicates; skip missing href and return an empty list if absent.

hrefs=source-order link hrefs with a rel token equal to preload

Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.

Output field	Meaning	Value type
hrefs	Matching link hrefs in document order.	list of string; maximum length: 1000000; minimum entries: 0; maximum entries: 100000

json

{
  "input": {
    "html": "<link rel=\"PRELOAD\" href=\"/app.js\"><link rel=\"stylesheet\" href=\"/style.css\">"
  },
  "output": {
    "hrefs": [
      "/app.js"
    ]
  }
}

Limitations and assumptions

The tool does not inspect as/type/crossorigin, fetch resources or resolve relative hrefs. Script-generated tags and full browser parsing recovery are outside this source scanner.

Numeric inputs must be finite. Follow the calculation-specific rules for overflow, underflow and exceptional cases. Extremely large text inputs are rejected. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use ModulepreloadDetector: Extract modulepreload link hints from HTML source without fetching, validating browser support, or resolving their hrefs. For a complementary task, use PreconnectHintParser: Extract preconnect link hints from HTML source without fetching, validating browser support, or resolving their hrefs.

References

LinkPreloadDetector — tool.io

Similar or alternative tools

ModulepreloadDetector
Extract modulepreload link hints from HTML source without fetching, validating browser support, or resolving their hrefs.
PreconnectHintParser
Extract preconnect link hints from HTML source without fetching, validating browser support, or resolving their hrefs.