PUDL Data Explorer Guide

This skill is for data users who want to explore, understand, and load PUDL's public energy data products. It assumes no access to the PUDL Python package or source repository — only the publicly distributed data files and their metadata.

PUDL's primary outputs are Apache Parquet files, described by a Frictionless Data Package descriptor. For generic descriptor-querying patterns (jq), use the datapackage skill — this skill provides PUDL-specific knowledge layered on top.

Beyond the main Parquet outputs, PUDL also distributes raw per-form FERC Parquet data (covering Forms 1/2/6/60/714, each with its own datapackage.json) and the FERC EQR (partitioned Parquet, separate from the main build). These have different access patterns and are not covered by the main Frictionless descriptor — see [Data Access](./references/data-access.md) for the full picture.

Workflow overview

Every step below is inexpensive and should happen by default whenever it's relevant to the question at hand, not only when the user asks for it by name.

1. Locate the metadata — the primary PUDL descriptor (Parquet outputs) is at:

- S3: s3://pudl.catalyst.coop/nightly/pudlparquetdatapackage.json - HTTPS: https://s3.us-west-2.amazonaws.com/pudl.catalyst.coop/nightly/pudlparquetdatapackage.json

Raw per-form FERC data has its own datapackage.json in each form/era directory, e.g. s3://pudl.catalyst.coop/nightly/ferc1xbrl/datapackage.json and s3://pudl.catalyst.coop/nightly/ferc1dbf/datapackage.json — see [Raw per-form Parquet directories](./references/data-access.md#raw-per-form-parquet-directories) for the full list.

The FERC EQR (Electric Quarterly Reports) is distributed separately due to its size, and only one version is publicly available at a time:

- S3: s3://pudl.catalyst.coop/ferceqr/ferceqrparquetdatapackage.json - HTTPS: https://s3.us-west-2.amazonaws.com/pudl.catalyst.coop/ferceqr/ferceqrparquetdatapackage.json

For offline or development use, download all descriptors locally with:

``bash python scripts/fetch_descriptor.py ``

This populates assets/cache/. The script is cache-aware — a cached file younger than a day is reused with no network call, so it's safe to run this every time you need a descriptor rather than checking assets/cache/ yourself first. Pass --force to bypass the cache and refetch regardless of age (e.g. if you suspect PUDL's schema changed today and need the very latest copy).

Raw input archives (for provenance) live at s3://pudl.catalyst.coop/zenodo/<dataset>/<concrete-doi>/datapackage.json. Prefer the cached S3 archive over the Zenodo website or API for raw metadata and file access. The source docs page usually gives a concept DOI for the whole dataset lineage; the S3 path uses a concrete DOI for one specific archived version. See [Data Quality and Context](./references/data-quality-and-context.md) for details.

1. Query metadata selectively — use /datapackage skill patterns (jq)

to find relevant tables, read descriptions, and surface warnings.

For "does PUDL have data on X" questions, don't stop at a match you already recognized by reputation — run a broader keyword sweep across relevant description/code fields first (for FERC accounts, see [Cross-referencing FERC Form 1 and Form 2 schedules and accounts](#cross-referencing-ferc-form-1-and-form-2-schedules-and-accounts); the same habit applies to other sources' core___codes_ tables). Flag it if an answer came from recalled knowledge rather than the sweep.

1. **Consult primary-source forms and instructions when metadata alone doesn't fully

explain something** — don't wait for the user to ask for these by name. See [Data Sources: Blank forms and filer instructions](./references/data-sources.md#blank-forms-and-filer-instructions).

1. Check table tier — see [Data Quality and Context](./references/data-quality-and-context.md).

Prefer out tables; warn users about core_ tables.

1. Check keys before joining tables — if the task combines a FERC-sourced table

with an EIA-sourced table (or any two tables at all), check schema.foreignKeys on each first, and route utility/plant joins through utilityidpudl / plantidpudl, not through name-string matching. See [PUDL Datapackage Extensions: Joining PUDL tables](./references/metadata-and-querying.md#joining-pudl-tables-use-declared-foreign-keys-and-pudls-id-crosswalks).

1. Check methodology before implementation details — if the user is asking how

PUDL cleans, imputes, allocates, reconciles, estimates, or models data, read [Methodology](./references/methodology.md) first and fetch the relevant public methodology page (append .md to the URL for your own reading — but when pointing the user to it, give them the plain .html link) before looking at source code, docstrings, or implementation details. Summarize the public methodology page and point the user to it. Only dive into code-level implementation after the user has seen that write-up or if no methodology page exists for the topic.

1. Load the data, efficiently — Loading data doesn't have to mean downloading an

entire table. SELECT ... LIMIT in DuckDB, pl.scan_parquet() with .select()/.filter() before .collect() in polars, and a columns= argument in pandas all push the selection down to the Parquet reader itself. Treat sampling and down-selecting as the normal way to explore a table, not an optimization reserved for when a file turns out to be huge. You should estimate a table's size before a full, unfiltered load, and only load the full table if the job genuinely needs every row; see [Data Access](./references/data-access.md) for the loading patterns themselves.

Reference index

• [Data Sources](./references/data-sources.md) — how to query the PUDL descriptor's own

sources array (31 datasets, with short codes, names, licensing, and per-source documentation links), and where to find and read each source's blank forms and filer instructions; read when a user asks about a specific source dataset (EIA-860, FERC Form 714, EPA CEMS, etc.) or needs documentation links, when resolving a raw-archive S3 path and you need the short code and have to distinguish between a concept-DOI and a concrete-DOI, or whenever interpreting what a column, code, or schedule actually means.

• [Data Access](./references/data-access.md) — S3 paths, loading patterns

(pandas/DuckDB/polars/pure SQL), raw per-form FERC Parquet locations, and EQR access; read whenever generating data-loading code or explaining how to access any PUDL output

• [PUDL Datapackage Extensions](./references/metadata-and-querying.md) — PUDL-specific

additions to the standard datapackage schema: RST/docstring-formatted descriptions, per-resource provenance fields, the package-level unit registry, and how to join tables across FERC/EIA ID systems via utilityidpudl/plantidpudl; read before querying description or other non-standard fields on a PUDL descriptor, and before joining any two PUDL tables (for generic descriptor-querying mechanics, use the datapackage skill instead)

• [Data Quality and Context](./references/data-quality-and-context.md) — table tier

naming conventions (out vs core vs raw), warning types, and what each tier means for analysis reliability; read when a user asks about data quality, when choosing between table tiers, or when surfacing warnings before providing loading code

• [Methodology](./references/methodology.md) — index of PUDL's data processing and

modeling methodology pages (entity resolution, timeseries imputation, ownership extraction); read when a user asks how PUDL cleans, reconciles, imputes, allocates, estimates, or models data. Fetch the specific public methodology page, summarize it, and point the user there before diving into implementation details from code or docstrings

• [FERC Electricity Accounts](./references/ferc-electricity-accounts.md) —

complete hierarchical chart of FERC electric utility accounts (balance sheet, electric plant, operating revenue, O&M expenses) with account numbers and descriptions; read when interpreting FERC Form 1 financial data or when a user asks what a specific account number means — prefer querying fercelectricityaccounts.json over reading this file

• [FERC Form 1 Schedules](./references/ferc1-schedules.md) — all 75 Form 1 schedules

with titles, descriptions, and table mappings; read when a user references a schedule by number or name (e.g. "Schedule 301", "Page 400a", "plant in service schedule") — prefer querying ferc1_schedules.json over reading this file

• [ferc1schedules.json](./assets/ferc1schedules.json) — query this first for any

FERC Form 1 schedule or table lookup; use jq to find schedules by keyword, account number, or PUDL table name without loading the full markdown into context

• [FERC Form 2 Schedules](./references/ferc2-schedules.md) — all 77 Form 2 schedules

with titles, descriptions, and XBRL table mappings (Form 2 is not yet integrated into PUDL); read when a user references a Form 2 schedule or asks about natural gas pipeline financial or operational data — prefer querying ferc2_schedules.json over reading this file

• [ferc2schedules.json](./assets/ferc2schedules.json) — query this first for any

FERC Form 2 schedule or table lookup; use jq to find schedules by keyword, account number, or XBRL table name without loading the full markdown into context

• [fercelectricityaccounts.json](./assets/fercelectricityaccounts.json) — query this first for any

FERC Form 1 (electric utility) account number lookup; use jq to resolve account definitions and cross-reference with Form 1 schedules via the ferc_accounts array

PUDL-specific constraints

• License: All PUDL data is published under the

Creative Commons Attribution 4.0 International (CC-BY-4.0) license. Users may freely use, share, and adapt the data with attribution to Catalyst Cooperative.

• Citation: When a user asks how to cite PUDL, provide this reference:

> Selvans, Z., Gosnell, C., Sharpe, A., Schira, Z., Lamb, K., Belfer, E., Xia, D., > & Mazaitis, K. The Public Utility Data Liberation (PUDL) Project [Data set]. > Catalyst Cooperative. <https://doi.org/10.5281/zenodo.3653158>;

BibTeX:

``bibtex @misc{pudl, author = {Selvans, Zane and Gosnell, Christina and Sharpe, Austen and Schira, Zachary and Lamb, Katherine and Belfer, Ella and Xia, Dazhong and Mazaitis, Kathryn}, title = {The Public Utility Data Liberation (PUDL) Project}, publisher = {Catalyst Cooperative}, doi = {10.5281/zenodo.3653158}, url = {https://doi.org/10.5281/zenodo.3653158}, } ``

• The S3 bucket s3://pudl.catalyst.coop is free and publicly accessible — no

AWS credentials needed, and any ambient credentials (even invalid ones) should be explicitly bypassed rather than assumed absent.

• **DuckDB, pandas, and polars each need explicit setup to query this bucket

reliably** — see [Data Access: DuckDB and S3](./references/data-access.md#duckdb-and-s3-required-setup) (s3urlstyle plus clearing S3 credential settings; applies through /query too) and the pandas/polars sections below it (storage_options for anonymous access) for why each is needed.

• The Parquet path for a core PUDL output table is

s3://pudl.catalyst.coop/nightly/<table_name>.parquet. Raw per-form FERC tables use a different path — see [Raw per-form Parquet directories](./references/data-access.md#raw-per-form-parquet-directories).

• Always surface usage warnings from the descriptor before providing loading code.

• Methodology-first rule: if a public methodology page exists for the topic the

user is asking about, use it before inspecting implementation details. Code-level explanations are a follow-up step, not the default first response.

• **Prefer out_* tables** for analyst work. If a user asks about a topic without

specifying a table, search metadata for out_ tables first.

• Use uv to install Python packages — prefer uv add <package> over

pip install <package>. uv is faster and installs into a virtual environment rather than globally. Fall back to pip only if uv is not available (command -v uv returns nothing) — and if you do, install into a project-local virtual environment (create one with python -m venv .venv if none exists), not the system/global Python. pip install --user is not a safe fallback either — it still writes into the user's global user-site packages, shared across every other project on their machine, rather than scoping the change to this task. If the working directory already has its own environment manager (pixi, poetry, an existing venv or conda env), install through that instead of introducing a second one.

• PUDL's datapackage descriptors extend the standard schema in several PUDL-specific

ways: RST-formatted, docstring-style descriptions, per-resource provenance metadata, and a package-level unit registry. Read [PUDL Datapackage Extensions](./references/metadata-and-querying.md) before writing jq queries against description or other non-standard fields — it covers only what's unique to PUDL; for generic descriptor-querying mechanics, use the datapackage skill.

• Prefer joining PUDL tables on ID columns over name-string columns

(utilitynameferc1, utilitynameeia, plant names, etc.) — same-named entities across FERC and EIA are not guaranteed to be the same company. Route joins through utilityidpudl / plantidpudl via the core_pudl__assn_* crosswalk tables, checking schema.foreignKeys first. Name matching is a legitimate fallback when no ID crosswalk is available, but treat its results as unverified until spot-checked. See [PUDL Datapackage Extensions: Joining PUDL tables](./references/metadata-and-querying.md#joining-pudl-tables-use-declared-foreign-keys-and-pudls-id-crosswalks).

Cross-referencing FERC Form 1 and Form 2 schedules and accounts

Both ferc1schedules.json and ferc2schedules.json share the same schema. Each record has a fercaccounts array with the account numbers that schedule references, pre-extracted for direct lookup. Use description for topical keyword search; use fercaccounts for account-number cross-referencing.

Quick lookup patterns (jq):

# Find all Form 1 schedules that reference a specific account number
jq '[.[] | select(.ferc_accounts[] == "182.3")] | .[] | {schedule, title}' \
    assets/ferc1_schedules.json

# Find all Form 2 schedules that reference a specific account number
jq '[.[] | select(.ferc_accounts[] == "489.2")] | .[] | {schedule, title}' \
    assets/ferc2_schedules.json

# Get all account definitions for a specific Form 1 schedule
SCHED="232"
jq --arg s "$SCHED" '.[] | select(.schedule == $s) | .ferc_accounts[]' \
    assets/ferc1_schedules.json |
xargs -I{} jq --arg a {} '.[] | select(.account == $a)' assets/ferc_electricity_accounts.json

Joining across both files (jq): load the accounts file with --slurpfile and use INDEX() to build an account-number lookup, then join it against each schedule's ferc_accounts array:

# Find PUDL tables and account definitions for a Form 1 topic (e.g. "regulatory assets")
jq --slurpfile accounts assets/ferc_electricity_accounts.json '
  ($accounts[0] | INDEX(.account)) as $acct_lookup
  | .[]
  | select(.description | test("regulatory asset"; "i"))
  | .schedule as $sched | .title as $title | .pudl_tables as $tables
  | .ferc_accounts[]
  | {schedule: $sched, title: $title, pudl_tables: $tables,
     account: ., account_description: $acct_lookup[.].description}
' assets/ferc1_schedules.json

# Find Form 2 XBRL tables for a topic (e.g. "storage") — single file, no join needed
jq '[.[] | select(.description | test("storage"; "i"))] |
    .[] | {schedule, title, xbrl_tables}' assets/ferc2_schedules.json

Delegation