Short answer
Open the file, confirm the tree shows what you expect, then copy the root value as JSON. Before you rely on the output, check merge keys, unquoted version numbers and very large integers.
Key points
- Blobster selects the top-level node when a file opens, and
Ctrl+C(Cmd+Con macOS) copies the selected value as JSON with two-space indentation. - A file that holds several documents separated by
---becomes a JSON array with one entry per document. - Anchors and aliases are expanded.
<<merge keys are not applied, so the shared mapping appears under a literal<<key. - Comments are dropped, because JSON has no comment syntax.
Steps
- Open the
.yamlor.ymlfile, drag it into Blobster or paste the text. - If pasted YAML opens as plain text, set Settings, Document, Format to YAML.
- Read the tree. Parse errors show the line, the column and an excerpt, so fix those first.
- With the top-level node selected, press
Ctrl+CorCmd+C. Select any branch instead to copy only that part. - Paste the JSON where you need it and check the cases below.
What changes on the way to JSON
Blobster reads YAML with the default YAML 1.2 rules of the yaml library. Most files convert exactly. A few common YAML habits produce JSON you might not expect.
| Case | YAML | JSON |
|---|---|---|
| Unquoted version number | version: 1.10 | "version": 1.1 |
| yes, no, on and off | enabled: yes | "enabled": "yes" |
| Dates | created: 2026-10-14 | "created": "2026-10-14" |
| Merge key | <<: *defaults | "<<": { ... } |
| Integer beyond 2^53 | id: 12345678901234567890 | "id": 12345678901234567000 |
Why two converters can disagree
YAML 1.1 treats yes, no, on and off as booleans. YAML 1.2 does not, so under Blobster’s default rules they stay strings. That is usually what you want for the on: key of a GitHub Actions workflow, which a YAML 1.1 parser turns into true.
A file that starts with a %YAML 1.1 directive is read with 1.1 rules instead. Merge keys then apply, and yes and on become true, including on when it is a key.
An unquoted 1.10 is a number in both versions, so it becomes 1.1. Quote version strings in the YAML if the trailing zero matters. Very large integers lose precision because the values become JavaScript numbers in the browser.
Merge keys need the tool that reads the file
Compose files can reuse settings with a merge key such as <<: *defaults. Merge keys are a YAML 1.1 feature that is not part of YAML 1.2, so Blobster expands the alias but leaves it under a << key instead of merging it into the service.
Compose’s documentation says it follows the YAML merge type. When you need the merged result, docker compose config --format json prints the model Compose will apply, as JSON.
When an online converter is fine
If the YAML is already public, such as an example from documentation, any converter will do. Blobster is for the files you should not paste into a website: Kubernetes manifests with internal hostnames, CI workflows, customer configs and anything with credentials in it. For conversions you repeat in a pipeline, use a command-line tool.