S3 Explore

For R2, if the user provides an account ID, the endpoint is <account_id>.r2.cloudflarestorage.com. R2 URLs like r2://bucket/path should be rewritten to s3://bucket/path with the R2 secret.

For public buckets (e.g., Overture Maps, AWS open data), no secret is needed — skip this step.

Always prepend:

LOAD httpfs;

Step 2 — Determine what the URL points to

If the URL looks like a directory or bucket (no file extension, or ends with /), list its contents with sizes:

duckdb -c "
LOAD httpfs;
<SECRET_SETUP>
SELECT filename, (size / 1024 / 1024)::DECIMAL(10,1) AS size_mb, last_modified
FROM read_blob('<URL>/*')
ORDER BY filename
LIMIT 50;
"

Note: only select filename, size, last_modified — never select content, which would download the actual files.

If the URL points to a specific file or glob pattern (has a file extension or contains *), preview it:

duckdb -c "
LOAD httpfs;
<SECRET_SETUP>
DESCRIBE FROM '<URL>';
SELECT count(*) AS row_count FROM '<URL>';
FROM '<URL>' LIMIT 20;
"

For Parquet files, get row counts and sizes from metadata (no data download):

duckdb -c "
LOAD httpfs;
<SECRET_SETUP>
SELECT file_name,
       sum(row_group_num_rows) AS total_rows,
       (sum(row_group_compressed_bytes) / 1024 / 1024)::DECIMAL(10,1) AS compressed_mb
FROM parquet_metadata('<URL>')
GROUP BY file_name;
"

Step 3 — Answer the question

Using the listing, schema, or sample data, answer:

${1:-list and describe what's there}

If the user asks an analytical question (e.g., "how many rows match X"), write and run the appropriate SQL query. DuckDB pushes predicates down into Parquet on S3, so filtering is efficient even on large remote datasets.

Error handling

• duckdb: command not found → delegate to /duckdb-skills:install-duckdb
• Access denied / 403 → suggest the user check credentials: aws configure, environment variables, or provide explicit key/secret
• Bucket not found / 404 → check the URL and region
• Timeout on large listing → suggest narrowing the glob pattern or adding a prefix