Compare two accessibility scans
diff_scanCompare two scans of the same page and report what changed: fixed[] (in the baseline, gone now), new[] (regressions — not in the baseline, present now), remaining[] (still there). Page-level complement to verify_fix (one element). Baseline is a scan_history id (baselineId, local installs) or a live scan of baselineUrl; current is url (scanned live now) or another history id (currentId). Live scans run a second time when they differ, and a difference that does not hold goes to unstable[], so a changed page can take twice as long. Findings are matched by issue id (rule + element), so a changed class/id on a fixed element reads as fixed AND new — check new[] before calling it a regression. Typical loop: scan_page → edit → diff_scan(baselineId=, url=) → confirm new[] is empty. NOTE: on this HOSTED server, localhost and private addresses are refused — it runs in our cloud and cannot reach your machine. Two ways to scan a local dev server: run the MCP locally (npx -y @webability/mcp, simplest — nothing leaves the machine), or open a tunnel (webability-tunnel --port 3000) and pass its URL as url together with the printed secret as tunnel_secret.
Tool call template
This tool declares no required parameters. Add optional parameters from the input schema as needed.
{
"id": 1,
"jsonrpc": "2.0",
"method": "tools/call",
"params": {
"arguments": {},
"name": "diff_scan"
}
}Input Schema
| Name | Required | Description | Default |
|---|---|---|---|
| url | No | URL to scan now as the CURRENT side (deployed, staging, or http://localhost:3000). Omit when passing currentId. | |
| wcag | No | Only these WCAG criteria. A prefix selects the whole guideline ("1.4") or principle ("2"). | |
| level | No | Highest WCAG conformance level to report. Default "AA" — Level AAA criteria are not reported. Pass "AAA" to include them (naming one AAA criterion in `wcag`, e.g. "3.2.5", also includes it). | |
| rules | No | Only these rule ids (WebAbility type such as "missing_alt" or axe rule id such as "image-alt"). See get_rules. | |
| format | No | "compact" prints one line per element with rule metadata once. "json" returns every field (html, fix values, source). Default: JSON when it fits inline (under ~24k chars), otherwise compact plus a JSON summary of every count. On the hosted server the default is compact. | |
| context | No | Explain in 15-25 words, in third person, why this tool is called and how it supports the user's goal. For analytics only. You MUST describe only the abstract purpose of the tool call. NEVER include, repeat, paraphrase, or infer personal, sensitive, or identifying information from the user request or tool results, including names, emails, phone numbers, IPs, IDs, or credentials. You MUST generalize specific entities into roles such as "a user", "the customer", or "an account". Example: "Retrieving a customer's recent orders to investigate a billing issue and help support determine the appropriate resolution." | |
| viewport | No | Viewport for live scans (default: desktop). Use the same viewport the baseline used. | |
| currentId | No | scan_history id to use as the CURRENT side instead of scanning `url` | |
| llm_model | No | The exact model identifier you (the assistant) are running as, taken from your system prompt or environment (e.g. "claude-opus-4-8", "gpt-5.2"). Used for analytics only. If you do not know your model identifier with certainty, pass "unknown" — never guess. | |
| minImpact | No | Only findings at this severity or above (critical > serious > moderate > minor) | |
| baselineId | No | scan_history id of the BASELINE scan (local installs only) | |
| baselineUrl | No | Scan this URL live as the baseline (e.g. production) — use when there is no stored baseline | |
| rootSelector | No | CSS selector to limit live scans to (optional) | |
| tunnel_secret | No | Secret printed by `webability-tunnel`. Required when `url` is a tunnel URL; the URL alone will be refused by the relay. Ignored otherwise. |