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vegafusion: Instructions file for Claude Code

CLAUDE.md

vegafusion CLAUDE.md is an instructions file for Claude Code from vega/vegafusion. It costs 407 tokens per session, scanned C, original, BSD-3-Clause.

A set of project instructions for VegaFusion, software that prepares data transformations for Vega charts before rendering them. It explains the Rust, Python, WebAssembly, and server components, setup commands, feature constraints, and testing approach.

In plain words
What is it for?
Use it when changing VegaFusion's Rust runtime, Python package, WebAssembly build, server, protocol files, error handling, or chart-output tests.
Why use it?
It helps prevent incompatible build settings and reminds developers to rebuild generated Python code after changing protocol definitions.

Instructions file for Claude Code

Written for Claude Code: the file is CLAUDE.md. Also seen: mentions CLAUDE.md.

This is vega/vegafusion's own configuration. It tells Claude Code how to work on vegafusion itself, so it is not a mod to install elsewhere. Copy it as a starting point and replace the rules that are about this project. Everything vegafusion configures →

not rated 425repo +1 7mo ago C scan 407 tokens original BSD-3-Clause
View source ↗ vega/vegafusion vegafusion.io
Reuse

Borrowing it

Nothing to install: this file belongs to vega/vegafusion. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file
curl -O https://raw.githubusercontent.com/vega/vegafusion/main/CLAUDE.md
Clone the repo
git clone --depth 1 https://github.com/vega/vegafusion

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

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Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

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Per session 407 This file is loaded in full into every session.
When invoked 407 The same file — it is already loaded in full.
Security scan C 2 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00407 $0.00407
Opus 5.5 $0.00163 $0.00163
Sonnet 5.5 $0.00081 $0.00081
Haiku 4.5 $0.00041 $0.00041

Measured 2mo ago against content hash 325e108775d9, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade C, and why

vegafusion CLAUDE.md scanned grade C with 2 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Downloads and executes remote codehighSupply chain

curl | sh runs whatever the server returns today, which is not necessarily what it returned when this was reviewed.

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh # Rust

Makes network callslowCapability

Not a fault in itself. Listed so you know the mod talks to something, and to what.

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh # Rust
CLAUDE.md · 52 lines

What it actually says

CLAUDE.md

VegaFusion optimizes Vega visualizations by pre-computing data transforms using Apache DataFusion. This enables scalable charting with the Vega ecosystem.

Architecture

Crate dependency chain:

  • vegafusion-common → vegafusion-core → vegafusion-runtime → (python, wasm, server)

DataFusion was chosen for columnar computation and query optimization capabilities.

Development Setup

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh  # Rust
curl -fsSL https://pixi.sh/install.sh | bash                     # Pixi (manages all else)

Key commands: pixi run test-rs-runtime, pixi run dev-py, pixi run build-wasm

Critical Constraints

IMPORTANT: Feature flag conflicts

  • http and http-wasm are mutually exclusive (use http-wasm for WASM builds)
  • tonic requires proto feature

IMPORTANT: Proto changes require Python rebuild

  • Proto files in vegafusion-core/src/proto/ auto-generate during build
  • After proto changes: pixi run dev-py

IMPORTANT: Error handling

  • Use .with_context(|| "message") pattern (see vegafusion-common for details)

Testing

Tests compare VegaFusion output against VegaJS reference implementation.

  • Float tolerance: 1e-6
  • Test specs: vegafusion-runtime/tests/specs/
  • VegaJS runtime: vegafusion-runtime/tests/util/vegajs_runtime/

Common Debugging

Proto compilation issues:

  • Check stderr for protoc errors
  • Verify protobuf-src feature if system protoc unavailable

Python "symbol not found":

  • Stale build - run pixi run dev-py

VegaJS test crashes:

  • Check npm install completed in tests/util/vegajs_runtime/
Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2mo ago First seen · 52 lines · 407 tokens per session scan C 325e108775d9

Subscribe to this mod's changes

vegafusion CLAUDE.md is an instructions file published in the GitHub repository vega/vegafusion (425 stars, last pushed 7mo ago), licensed BSD-3-Clause. It adds 407 tokens to every session, about $0.0016 per session on Opus 5.5. A static security scan graded it C with 2 findings (downloads and executes remote code, makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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