Markback

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MarkbackComments for anything.

In plain text. In git. Markback is a tiny text format for leaving feedback on any file — text, code, images, PDFs. Lints, diffs, and lives next to the work.

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Install
Format Spec
GitHub
Markback

Anywhere

Annotate any file via inline records or name.ext.mb sidecars — text, code, Markdown, images, PDFs, audio.

One delimiter

<<< is the whole syntax. No schema to pick, no app to install. Hand-writable and lintable.

Diffable

Records live in your repo. Lint, normalize, version them alongside the work they annotate.

Reach for the runtime you use

Python, Node, CLI, browser editor, and a VS Code extension.

Try it without installing ​

The browser editor below uses the same markbackjs lint engine the CLI uses. Paste your own content, leave comments with <<<, and watch the diagnostics update as you type.

Open the live editor →

How it works in 30 seconds ​

Three ways to capture a comment. One delimiter. All lint to the same shape.

┌──────────────────┐    ┌──────────────────┐    ┌──────────────────┐
│  inline          │    │  compact         │    │  sidecar         │
│                  │    │                  │    │                  │
│  the lazy fox    │    │  @file ./img.jpg │    │  report.pdf      │
│  <<< awkward     │    │  <<< approved    │    │  report.pdf.mb   │
└────────┬─────────┘    └────────┬─────────┘    └────────┬─────────┘
         │                       │                       │
         └───────────────────────▼───────────────────────┘
                        ┌────────────────┐
                        │   mb --lint    │   parse · validate
                        │   mb --normalize │ canonicalize
                        └────────────────┘

Inline records keep the comment next to the content. Compact records put @file and <<< on one line — great for batch labeling. Sidecar files (report.pdf.mb) let you comment on anything, even binary files.

Quick example ​

mb
%markback 2

@id prompt-001
@tag training

# API Design Task

Create an endpoint that:

- **GET** `/users/{id}`
- Returns JSON with `name`, `email`
- Handle 404 for missing users
<<< approved; clarity=high; needs=error examples

The content (Markdown) stays readable. The <<< line captures feedback that lints, diffs, and survives a git blame. Try it live →

What problem it solves ​

Prompt iteration usually scatters content, labels, and reviewer notes across JSON, spreadsheets, and ad-hoc scripts. Markback standardizes the feedback loop in a text format that works in Git, can be linted, and scales from a single prompt to thousands of records.

Common questions ​

  • FAQ — "How is this different from JSONL?" / "Why two packages?" / "Can I annotate images?"
  • Comparison — Markback vs JSONL labels, Label Studio, doccano, Argilla.