fibrum-pdf 1.0.3

A fast PDF extractor; a 500 pages/s alternative to Marker, Docling, PyMUPDF4LLM & others.

FibrumPDF

This projects C extension has now been rewritten in Go. Performance, quality, and code quality have all improved. However, the Python-API remains the same. It's also been renamed from PyMUPDF4LLM-C, because that was way too close to PyMuPDF4LLM.

A fast PDF extractor for Python written in Go using MuPDF in the backend, inspired by pymupdf4llm. I took many of its heuristics and approaches. Initially, it was supposed to be a 1:1 port (just generating the same Markdown output), but I later pivoted.

Most extractors give you raw text (fast but useless) or full-on OCR/ML. This is a middle ground.

Outputs JSON for every block: text, type, bounding box, font metrics, tables. You get the raw data to process however you need.

Speed (averaged): ~520 pages/second on CPU. 1 million pages in ~32 minutes.

Full performance breakdown here

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Installation

pip install fibrum-pdf

You can prefix this with whatever tools you use, like uv, poetry, etc.

There are wheels for Python 3.9–3.14 (inclusive of minor versions) on macOS (ARM/x64) and all modern Linux distributions.

To build from source, see BUILD.md.

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What it's good at

• millions of pages, fast
• custom parsing logic; you own the rules
• document archives, chunking strategies, any structured extraction
• CPU only; no expensive inference
• iterating on parsing logic without waiting hours

What it's bad at

• scanned or image-heavy PDFs (no OCR)
• 99%+ accuracy on edge cases; trades precision for speed
• figures or image extraction

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Usage

basic

from fibrum_pdf import to_json

result = to_json("example.pdf", output="example.json")
print(f"Extracted to: {result.path}")

You can omit the output field; it defaults to <file>.json

collect all pages in memory

result = to_json("report.pdf", output="report.json")
pages = result.collect()

# Access pages as objects with markdown conversion
for page in pages:
    print(page.markdown)
    
# Access individual blocks
for block in pages[0]:
    print(f"Block type: {block.type}")
    print(f"Has {len(block.spans)} spans")

This still saves it to result.path; it just allows you to load it into memory. If you don't want to write to disk at all, consider providing a special path.

This is only for smaller PDFs. For larger ones, this may result in crashes due to loading everything into RAM. See below for a solution.

stream pages (memory-efficient)

result = to_json("large.pdf", output="large.json")

# Iterate one page at a time without loading everything
for page in result:
    for block in page:
        print(f"Block type: {block.type}")

convert to markdown

result = to_json("document.pdf", output="document.json")
pages = result.collect()

# Full document as markdown
full_markdown = pages.markdown

# Single page as markdown
page_markdown = pages[0].markdown

# Single block as markdown
block_markdown = pages[0][0].markdown

.markdown is a property, not a function

command-line

python -m fibrum_pdf.main input.pdf [output_dir]

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Output structure

Each page is a JSON array of blocks. Every block has:

• type: block type (text, heading, paragraph, list, table, code)
• bbox: [x0, y0, x1, y1] bounding box coordinates
• font_size: font size in points (average for multi-span blocks)
• length: character count
• spans: array of styled text spans with style flags (bold, italic, mono-space, etc.)

Note that a span represents a logical group of styling. in most blocks, it is likely that there is only one span.

Block types

Not real JSON; just to demonstrate output. (pseudo).

text/paragraph/code blocks:

{
  "type": "text",
  "bbox": [72.03, 132.66, 542.7, 352.22],
  "font_size": 12.0,
  "length": 1145,
  "lines": 14,
  "spans": [
    {
      "text": "Block content here...",
      "font_size": 12.0,
      "bold": false,
      "italic": false,
      "monospace": false,
      "strikeout": false,
      "superscript": false,
      "subscript": false,
      "link": false,
      "uri": false
    }
  ]
}

headings:

{
  "type": "heading",
  "bbox": [111.80, 187.53, 509.10, 217.56],
  "font_size": 32.0,
  "length": 25,
  "level": 1,
  "spans": [
    {
      "text": "Heading Text",
      // all styling flags (as seen in the above)
    }
  ]
}

lists:

{
  "type": "list",
  "bbox": [40.44, 199.44, 107.01, 345.78],
  "font_size": 11.04,
  "length": 89,
  "spans": [],
  "items": [
    {
      "spans": [
        {
          "text": "First item",
		  // all styling flags.
        }
      ],
      "list_type": "bulleted",
      "indent": 0,
      "prefix": false
    },
    {
      "spans": [
        {
          "text": "Second item",
		  // all styling flags.
        }
      ],
      "list_type": "numbered",
      "indent": 0,
      "prefix": "1."
    }
  ]
}

tables:

{
  "type": "table",
  "bbox": [72.0, 220.0, 523.5, 400.0],
  "font_size": 12.0,
  "length": 256,
  "row_count": 3,
  "col_count": 2,
  "cell_count": 2,
  "spans": [],
  "rows": [
    {
      "bbox": [72.0, 220.0, 523.5, 250.0],
      "cells": [
        {
          "bbox": [72.0, 220.0, 297.75, 250.0],
          "spans": [
            {
              "text": "Header A",
              // all styling flags.
            }
          ]
        },
        {
          "bbox": [297.75, 220.0, 523.5, 250.0],
          "spans": [
            {
              "text": "Header B",
              // all styling flags.
            }
          ]
        }
      ]
    }
  ]
}

Span fields

all text spans contain:

• text: span content
• font_size: size in points
• bold, italic, monospace, strikeout, superscript, subscript: boolean style flags
• link: boolean indicating if span contains a hyperlink
• uri: URI string if linked, otherwise false

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FAQ

why not marker/docling?
if you have time and need maximum accuracy, use those. this is for when you're processing millions of pages or iterating on extraction logic quickly.

how do i use bounding boxes for semantic chunking?
large y-gaps indicate topic breaks. font size changes show sections. indentation shows hierarchy. you write the logic using the metadata.

will this handle my complex PDF?
optimized for well-formed digital PDFs. scanned documents, complex table structures, and image-heavy layouts won't extract as well as ML tools.

commercial use?
only under AGPL-v3 or with a license from Artifex (MuPDF's creators). see LICENSE

why did you build this? Dumb reason. I was building a RAG project with my dad (I'm 15). He did not care about speed at all. But I just got bored of waiting for chunking the PDFs every time I made a minor change. I couldn't find anything with even 50% of the quality that would be faster. And anyway, my chunks were trash. So it was either: raw text, or ML, and I didn't want either of them.

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Performance Breakdown

Using go/cmd/tomd/main.go with input_pdf [output_dir], I measured performance on:

• ~1600 page document (path not available)
• ~150 page document (test_data/pdfs/nist.pdf)

Performance depends on document size and available cores. With more pages to saturate your cores, you may see better throughput. Wall-clock time should scale approximately linearly with core count.

Test system: AMD Ryzen 7 4800H (8 cores, 6 used)

Runtime breakdown:

• Go code: ~25% of runtime
• MuPDF: ~75% of runtime

On the NIST document (150 pages): Go spent 78ms out of 363ms total (21%), MuPDF spent 285ms (79%).

Calculated average:

• 1600 pages in 3000ms + 150 pages in 350ms = 1750 pages in 3350ms
• ~520 pages/second

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Licensing and Links

licensing

TL;DR: use it all you want in OSS software. if you buy license for MUPDF from Artifex, you are excluded from all AGPL requirements.

• derived work of mupdf.
• inspired by pymupdf4llm; i have used it as a reference

AGPL v3. commercial use requires license from Artifex.

modifications and enhancements specific to this library are 2026 Adit Bajaj.

see LICENSE for the legal stuff.

links

• repo: github.com/intercepted16/fibrum-pdf
• pypi: fibrum-pdf