---

name: webspec-index description: Use webspec-index to query WHATWG, W3C, IETF and TC39 web specifications from the command line

webspec-index

Query WHATWG, W3C, IETF and TC39 web specifications from the command line.

Use webspec-index whenever you need to understand what a web spec says — algorithm steps, section content, cross-references, or whether a spec anchor exists. Specs are fetched and cached locally on first use.

Available specs

Assume that all specs from WHATWG, W3C, IETF and TC39 are indexed. If in doubt, run webspec-index specs to list all spec names and their base URLs.

Installation

If webspec-index is not already available in your environment, you can install it via cargo:

cargo binstall webspec-index
# or
cargo install webspec-index

Commands

Always put the section identifier in quotes to avoid shell interpretation of #.

See webspec-index --help for full command list and options.

Look up a spec section

webspec-index query 'HTML#navigate'
webspec-index query 'DOM#concept-tree'
webspec-index query 'CSS-GRID#grid-container'
webspec-index query 'https://html.spec.whatwg.org/#navigate'
webspec-index query 'DOM#concept-tree'
webspec-index query "RFC9000#section-22"
webspec-index query "draft-ietf-tsvwg-sctp-dtls-chunk#name-security-considerations"
webspec-index query 'https://w3c.github.io/webappsec-permissions-policy/#permissions-policy-header'

Returns the section's title, type (heading/algorithm/definition), full content as markdown, navigation tree (parent/prev/next/children), and cross-references. This is the primary command — use it to read what a spec section says.

Use --format markdown for human-readable output, or default --format json for structured data. For non-hardcoded specs, URL queries are accepted for allowlisted domains (*.spec.whatwg.org, drafts.csswg.org, w3c.github.io, wicg.github.io, webaudio.github.io, tc39.es, w3.org/TR/*, and webassembly.github.io).

Search across specs

webspec-index search "tree order"
webspec-index search "navigate" --spec HTML --limit 5

Full-text search with snippets. Use --spec to narrow to one spec.

Check if a section exists

webspec-index exists 'HTML#navigate'

Exit code 0 = found, 1 = not found. Use this to validate anchor names before referencing them.

Find anchors by pattern

webspec-index anchors "*-tree" --spec DOM
webspec-index anchors "concept-*" --spec HTML
webspec-index anchors "dom-*assign*"

Glob matching (* wildcard). Useful when you know part of an anchor name but not the exact id.

List all sections in a spec

webspec-index list DOM

Returns all heading-level sections with their anchors, titles, types, and depths.

Cross-references

webspec-index refs 'HTML#navigate' --direction incoming
webspec-index refs 'HTML#navigate' --direction outgoing
webspec-index refs 'HTML#navigate'
webspec-index refs 'Window.navigation' --limit 5

Shows which sections reference this one (incoming), which sections this one references (outgoing), or both (default). Target can be exact (SPEC#anchor or full URL) or shorthand (Interface.member) resolved heuristically against currently indexed sections. Use --limit to cap results when using shorthand queries.

WHATWG PR previews

webspec-index query 'HTML#navigate' --pr 12345
webspec-index query 'HTML#navigate' --pr 12345 --diff --format markdown
webspec-index query 'HTML#navigate' --pr 12345 --force-update
webspec-index exists 'HTML#navigate' --pr 12345
webspec-index list HTML --pr 12345
webspec-index refs 'HTML#navigate' --pr 12345
webspec-index search 'OpaqueRange' --spec HTML --pr 12345
webspec-index anchors '*opaquerange*' --spec HTML --pr 12345

Query spec sections as modified by an open WHATWG PR. Previews are lazily fetched from whatpr.org on first use and cached for 24h.

• --pr N: query the spec as it would look after PR N is merged. Sections not modified by the PR fall back to the merge base.
• --diff: show a section-level diff between the PR and its merge base. Lists added/modified sections with unified diffs.
• --force-update: re-fetch the PR preview even if recently cached (use after the PR is updated).

Manage cached PR data with clear-pr:

webspec-index clear-pr                         # list cached PRs
webspec-index clear-pr --spec HTML --pr 12345  # remove one PR
webspec-index clear-pr --all                   # remove all

Update specs

webspec-index update
webspec-index update --spec HTML
webspec-index update --force

Fetches latest spec versions. Uses 24h cache unless --force is given. Specs are auto-fetched on first query, so you rarely need this. Specs are checked on a 24h cadence; re-indexing happens only when fetched HTML content changed.

Graph traversal

webspec-index graph 'HTML#navigate' --direction outgoing --max-depth 2
webspec-index graph 'HTML#navigate' --graph-format mermaid
webspec-index graph 'HTML#navigate' --graph-format dot
webspec-index graph 'HTML#navigate' --same-spec-only
webspec-index graph 'HTML#navigate' --include '*concept-*' --exclude 're:^URL#'

Builds a cross-reference graph rooted at a section. Supports JSON (default), Markdown, Mermaid, and Graphviz DOT output. Use --include and --exclude to filter node ids (SPEC#anchor) by wildcard patterns (*, ?) or regex (re:<pattern>).

Query dedicated WebIDL definitions

webspec-index idl 'HTML#dom-window-navigation'
webspec-index idl 'Window.navigation'
webspec-index idl 'Window.open()'
webspec-index idl 'navigation' --spec HTML --limit 5

Queries structured WebIDL definitions directly. Supports exact anchors (SPEC#anchor or URL) and canonical names (Interface.member, Interface.method()). Use this first when the task is about API shape or IDL ownership, then use refs to see algorithm usage.

Usage patterns for Gecko development

Understanding what you're implementing

When working on a bug that references a spec algorithm:

# Read the algorithm you need to implement
webspec-index query 'HTML#navigate' --format markdown

# Check what concepts it references
webspec-index refs 'HTML#navigate' --direction outgoing

# Look up a referenced concept you don't understand
webspec-index query 'INFRA#ordered-set'

Finding the right spec section

When you see a spec URL in code comments (e.g., https://html.spec.whatwg.org/#navigate), or a step comment like // Step 3.2, query the section to understand the algorithm:

webspec-index query 'https://html.spec.whatwg.org/#navigate'

When you know a concept but not its exact anchor:

# Search by text
webspec-index search "tree order" --spec DOM

# Or find by anchor pattern
webspec-index anchors "*tree*order*" --spec DOM

Verifying spec anchors

Before adding a spec URL to a code comment, verify the anchor exists:

webspec-index exists 'HTML#navigate' && echo "valid"

Understanding cross-spec dependencies

To see what other specs depend on a concept you're changing:

webspec-index refs 'DOM#concept-tree' --direction incoming

Tracing IDL API usage in algorithms

When implementing or reviewing a DOM API in Gecko:

# Find canonical IDL definition + owning interface
webspec-index idl 'Window.navigation' --format markdown

# Find where the property is used in indexed specs
webspec-index refs 'Window.navigation' --direction incoming

Finding where Gecko implements a spec section

When the user asks where a spec algorithm is implemented in Gecko or SpiderMonkey, query the spec section first, then pass the url field from the response to searchfox-cli:

# Step 1 — read the spec section (response includes a "url" field)
webspec-index query 'HTML#navigate' --format json

# Step 2 — find Gecko source files that reference that URL
searchfox-cli --spec-refs 'https://html.spec.whatwg.org/#navigate'

Always do this when the user asks questions like "where is X implemented", "which file handles Y", or "show me the Gecko code for Z". The url field in the query response is the value to pass to --spec-refs — no manual URL construction needed.

Implementing a feature from a spec PR

When the bug references a spec PR that hasn't landed yet:

# See what the PR changes at a section level
webspec-index query 'HTML#navigate' --pr 12345 --diff --format markdown

# Read the algorithm as modified by the PR
webspec-index query 'HTML#navigate' --pr 12345 --format markdown

# Check what new cross-references the PR introduces
webspec-index refs 'HTML#navigate' --pr 12345 --direction outgoing