vizier

Chart judgment for people and agents. Most bad charts aren't ugly — they're a defensible-looking answer to a question nobody asked, or an honest-looking answer the data can't support. Both failures happen before the first line of plotting code. vizier moves that decision onto something documented: it picks the chart form from the reader's question, runs the checks a graphics desk runs before publishing, and — with a corpus of critical writing — judges what a finished chart got wrong.

It answers the parts of a chart that are actually decidable, and refuses the ones that aren't honest. It's built to be called by an agent or a generator, so the tool asks vizier for the decision instead of re-deriving it from a half-remembered rule.

Install

The primary path is the Claude Code plugin, where vizier fires before a chart gets built:

/plugin marketplace add lyra-forge/marketplace
/plugin install vizier@lyra-forge

Two skills — chart-design (decide a chart) and chart-critique (judge one) — plus vizier's MCP server, so the same answers are available as tools. The skills drive the vizier CLI, which installs separately:

uv tool install datavizier        # or: pip install datavizier
vizier doctor                     # what's live, what's missing, and how to fix it

The PyPI distribution is datavizier (the bare name was taken); the import package and command are both vizier — import vizier, vizier …. Python 3.12+.

pip install datavizier                 # the toolkit, pattern library, and MCP server
pip install "datavizier[search]"       # + semantic retrieval (find_similar)
pip install "datavizier[critique]"     # + LLM critique/eval (needs an LLM gateway; see below)
pip install "datavizier[ingest]"       # + rebuild the corpus from source

The core has no proprietary and no heavyweight dependencies, and needs no key and no network: form recommendation, the journalism checks, the pattern library, structural analysis, and color all work from pip install datavizier alone. The 43 chart-form patterns ship inside the package; the index builds itself on first use.

Quickstart

# decide — give me one that's right
vizier recommend-form "how a budget splits, across five districts" --n-series 5
vizier patterns show stacked-bar         # when to use, when NOT, mistakes, checklist
vizier guide "per-pupil spending vs the state average" --context "<headline>"

# critique — is this one right?
vizier analyze chart.svg                 # structural + color checks from the artifact
vizier critique chart.png                # corpus-backed review (optional extra + key)

# color, once
vizier suggest-palette 6                 # a CVD-safe categorical palette, validated
vizier suggest-ramp 5 --hue navy         # a one-hue ordinal ramp, validated
vizier validate "#e69f00,#0072b2,#009e73" --pairs all
vizier ink "#0072b2"                     # the legible text color for a fill

recommend-form returns the form that fits with its when_not_to_use list and the alternatives that name your situation — the alternatives are where the judgment is. guide returns the honesty checks for the job: the benchmark that makes a number interpretable, percent of what and dollars per whom, the most likely wrong reading and where you're blocking it.

Color is the last five percent, and it's handled: every palette is validated before it's returned (colorblind ΔE via Machado-2009, WCAG contrast, OKLCH lightness/chroma), and a request that can't be satisfied honestly errors rather than returning something that fails. See docs/computed-color-checks.md.

MCP server

vizier mcp serves everything above (plus the corpus query) as an MCP stdio server, so Claude Code / Cursor / any MCP client can call it. The plugin registers it for you; elsewhere:

claude mcp add vizier -- vizier mcp

Tools: recommend_form, implementation_guide, list_patterns, get_pattern, analyze_artifact, validate_palette, suggest_palette, suggest_ramp, ink_on, check_contrast, plus corpus query (search, find_similar, list_rubrics, …). Setup + troubleshooting: docs/mcp-setup.md.

Chart pattern library + reader

vizier ships 43 chart-form patterns (FT Visual Vocabulary families) — each with when-to-use / when-not / alternatives / common-mistakes / reading-checklist. Browse them or route to one:

vizier patterns list --family Flow
vizier patterns show sankey

docs/reader/ is a self-contained static guide (open docs/reader/index.html, or the published site) that renders the whole library with live d3 demos, generated from the pattern data (vizier patterns export -o docs/reader/data.json). It vendors its own d3 and design tokens — no build step, no external dependencies.

Corpus (rebuild your own)

vizier's critique is sharpened by a corpus of data-viz writing (award commentary, critique blogs, practitioner walkthroughs). Only vizier's own authored content ships — the 43 patterns, the rubrics, the FT-vocabulary parse, and the weaver principles. The third-party sources are not redistributed (they're copyrighted); rebuild them locally:

vizier ingest all        # fetch + parse into corpus/<source>/
vizier db build --embed  # index for search + retrieval

Set VIZIER_CORPUS_ROOT=/absolute/path/to/corpus-root before running vizier ingest or vizier db build to write/read a corpus outside the installed package tree. This is how the private corpus artifact is rebuilt without copying private source material into the public package. VIZIER_DB_PATH overrides where the index itself lives (default: beside the corpus in a checkout, or a per-user cache directory for a packaged install).

What the corpus draws on and why is described in INFLUENCES.md; the per-source ingest notes are in docs/process-notes-sources.md. Fetching is pluggable (src/vizier/ingest/_common.py): the bundled default is httpx; point $VIZIER_FETCHER at a richer fetcher, or set your own FETCHER.

If you keep a private or local corpus DB with the same schema, keep it out of the distributed package and point vizier at it at runtime — this is the plug point for proprietary prior art, so nothing private ever ships in the public package:

VIZIER_PRIVATE_DB=/absolute/path/to/private/.vizier.db vizier db search "reader decision"
VIZIER_EXTENSION_DBS=/absolute/path/to/private/.vizier.db vizier db search "reader decision"
VIZIER_EXTENSION_DBS="/path/one.db:/path/two.db" vizier mcp

Extension DBs are opened read-only and merged into the read-side corpus APIs: search, find_similar, lookup, list_sources, list_principles, list_rubrics, list_patterns, get_pattern, and stats. VIZIER_EXTRA_DB_PATHS is accepted as an alias for the same path-list. As a convenience, vizier also auto-discovers an extension DB in a sibling vizier-private/corpus/vizier-private.db; set VIZIER_AUTO_PRIVATE=0 to disable that and run against the public corpus only.

Critique + evaluation (optional)

vizier critique <image> and the vizier eval harness use an LLM. vizier routes calls through somm (an LLM gateway); provide a key in .env (copy .env.example) — vizier reads .env from the working directory upward. vizier doctor names exactly what's missing. The color-CVD case under evals/ demonstrates the measured lift from the computable findings — see docs/computed-color-checks.md.

The vizier ↔ weaver split

vizier is the critique + decision companion to weaver, which renders graphics. weaver draws the pixels; vizier decides which form and which colors, and judges the result. The same thresholds serve both directions — see PRINCIPLES.md.

Development

uv sync
uv run pytest -q            # also runnable per-file: python tests/test_color.py
uv run ruff check src/ tests/
tests/install/run.sh        # what a *user's* install does — see tests/install/README.md

All three run in CI on every PR and push (.github/workflows/ci.yml, Python 3.12–3.13). The install test is the one that catches what a source checkout hides: whether the corpus travelled in the wheel, whether the MCP server starts, whether the plugin installs, and whether the optional paths explain themselves when they can't run.

MIT licensed. Contributions welcome — see CONTRIBUTING.md. Release process and versioning: RELEASING.md; notable changes: CHANGELOG.md.