---
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:
```bash
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
```bash
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
```bash
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
```bash
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
```bash
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
```bash
webspec-index list DOM
```
Returns all heading-level sections with their anchors, titles, types, and depths.
### Cross-references
```bash
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
```bash
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`:
```bash
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
```bash
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
```bash
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
```bash
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:
```bash
# 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:
```bash
webspec-index query 'https://html.spec.whatwg.org/#navigate'
```
When you know a concept but not its exact anchor:
```bash
# 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:
```bash
webspec-index exists 'HTML#navigate' && echo "valid"
```
### Understanding cross-spec dependencies
To see what other specs depend on a concept you're changing:
```bash
webspec-index refs 'DOM#concept-tree' --direction incoming
```
### Tracing IDL API usage in algorithms
When implementing or reviewing a DOM API in Gecko:
```bash
# 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`:
```bash
# 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:
```bash
# 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
```
