The full upstream README, mirrored here for reference. Install config, tool schemas, adoption signals, and an original overview live on the Browser Compat MCP Server listing page.
Browser compatibility and Baseline status for any web feature — offline, from MDN's browser-compat-data, web-features, and caniuse. STDIO or Streamable HTTP.
Public Hosted Server: https://browser-compat.caseyjhand.com/mcp
Web platform compatibility for frontend work: per-browser support from MDN's @mdn/browser-compat-data, Baseline state and dates from web-features, and browserslist target resolution weighted by caniuse-lite usage figures. Every dataset ships inside the package, so there are no runtime network calls, no API key, no rate limit, and no upstream to be down — the same answers come back air-gapped. Runs as a stdio process, a local Streamable HTTP server, or the public hosted endpoint above.
| Tool | Description |
|---|---|
browsercompat_list_reference | Enumerate the reference vocabulary the other tools expect — BCD namespaces and browser ids, browserslist agents, Baseline states, groups, and ECMAScript snapshots. |
browsercompat_get_feature | Full compatibility record for one feature: Baseline state, standards status, per-browser versions with flags and prefixes, MDN and specification links. |
browsercompat_check_baseline | Ship-or-not across up to 20 features: Baseline state and date, the limiting browser, deprecation flags, and the traffic share requiring it would exclude. |
browsercompat_search_features | Find features by plain name, keyword, or code notation when the canonical key is unknown, ranked with the field that matched, filterable by group or ECMAScript snapshot, and pageable. |
browsercompat_compare_support | Check features against an explicit browserslist target query, reporting the failing target per feature and every target that could not be evaluated. |
browsercompat_list_reference tooltopic: bcd_namespaces (12), bcd_browsers (17), browserslist_agents (19), baseline_states (4), groups (104), or snapshots (11). Group and snapshot ids feed the search filters.id, label, and detail, plus count, reported, bcd_browser, usage_percent, maps_from, or spec_url where applicable. An agent's bcd_browser: null means support comparisons cannot evaluate it and report it in unchecked_targets.browsercompat_get_feature toolfeature, 1–200 characters: a BCD key (css.selectors.has) or web-features id (has). resolve: true accepts a name or notation only when the best exact matches name one feature: one key resolves directly, several keys of one feature return compat_keys, and two features are a miss. Off by default.outcome is found, no_compat_data, or miss; resolved_as records the match. A miss returns found: false with guidance. A multi-key id omits support, status, limiting_browser, mdn_url, and spec_urls; use compat_keys for a specific call. Whitespace-only input returns invalid_feature_input.include_runtimes: true adds bun, deno, nodejs, and oculus support to the 13 desktop and mobile browser rows.browsercompat_check_baseline toolinvalid_feature_input.limiting_browser, deprecated, experimental, discouraged, and usage_percent_excluded with its usage_source. Usage is absent, never zero, when no caniuse id exists.all_widely_available requires every entry to resolve at widely; one miss makes it false, and it does not assess deprecation.browsercompat_search_features toolquery, 1–100 characters, accepts names, keywords, or notation such as Array.prototype.at, display: grid, or <dialog>. Combine namespace (12 BCD namespaces), baseline (widely, newly, limited, not_mapped), group (including nested groups), and snapshot (such as ecmascript-2023).matched_on explains the six-tier ranking; path_suffix marks trailing key segments matching the supplied notation. support_summary covers the seven Baseline core browsers (— unsupported, ? unknown). Typed failures: invalid_query (zero searchable tokens), unknown_group, unknown_snapshot.limit (1–50, default 10) and offset (default 0); totalCount counts all matches and nextOffset appears while more remain. Zero hits succeed with a notice naming which filter to drop; an offset past the matches returns an empty page with a notice.browsercompat_compare_support tooltargets browserslist query, such as defaults or > 0.5%, last 2 versions; local browserslist config is never used. Typed failures: invalid_target_query, no_targets_resolved, invalid_feature_input.verdict is clears, fails, inconclusive, miss, or ambiguous. failing_targets names targets with partial, prefixed, flagged, removed, unsupported, or preview_only support.unchecked_targets carries no_bcd_browser, unknown_version, or no_bcd_data; all_clear requires it to be empty. The response also includes caniuse-derived target_coverage_percent and unchecked_coverage_percent.| Package | Version | License | Supplies |
|---|---|---|---|
@mdn/browser-compat-data | ^8.1.2 | CC0-1.0 | Per-browser support, standards status, MDN and specification links |
web-features | ^3.39.0 | Apache-2.0 | Baseline state and dates, discouraged flags, groups, ECMAScript snapshots |
caniuse-lite | ^1.0.30001810 | CC-BY-4.0 | Usage weighting, plus feature titles for the search index |
browserslist | ^4.29.0 | MIT | Target query resolution and coverage figures |
CC BY 4.0 requires attribution wherever the caniuse data travels, so every response carrying a usage figure carries this string: Usage data from caniuse.com, © Can I Use contributors, CC BY 4.0. Figures are a share of the ~96.7% of global traffic caniuse tracks. Full license texts and notices are in THIRD_PARTY_NOTICES.md.
Built on @cyanheads/mcp-ts-core: stdio and Streamable HTTP transports, pluggable auth (none / jwt / oauth), swappable storage (in-memory, filesystem, Supabase, Cloudflare KV/R2/D1), structured logging with optional OpenTelemetry tracing.
Browser-compat-specific:
status.by_compat_key, never rolled up from the feature level, because keys under one feature legitimately disagreemoved redirect, and only under resolve: true the search index's best exact matches, when they name one featuresafari 16.0 ↔ 16, samsung 20 ↔ 20.0)Agent-friendly output:
data_version — the version of each bundled dataset behind the answer, since a pinned snapshot goes stale on exactly the newest featuresunchecked_targets and the feature to inconclusivefound: false with guidance naming the next call, and typed error reasons carrying recovery hints for the input a caller has to fixA public instance is available at https://browser-compat.caseyjhand.com/mcp — no installation required. Point any MCP client at it via Streamable HTTP:
Add the following to your MCP client configuration file:
Or with npx (no Bun required):
Or with Docker:
For Streamable HTTP, set the transport and start the server:
There are no server-specific environment variables: no API keys, no base URLs, and deliberately no browserslist configuration variable — the target query is always a tool input rather than ambient state. Framework transport, logging, and telemetry settings remain configurable.
| Variable | Description | Default |
|---|---|---|
MCP_TRANSPORT_TYPE | Transport: stdio or http. | stdio |
MCP_HTTP_PORT | Port for the HTTP server. | 3010 |
MCP_SESSION_MODE | HTTP session mode, explicitly set by .env.example and Docker. When unset, the framework's auto fallback resolves to stateful. | stateless |
OTEL_ENABLED | Enable OpenTelemetry; local installs need the framework's optional telemetry peers. Docker includes them by default. | false |
OTEL_EXPORTER_OTLP_ENDPOINT | Base URL for traces (/v1/traces) and metrics (/v1/metrics); signal-specific endpoints override it. | Unset |
OTEL_EXPORTER_OTLP_LOGS_ENDPOINT | Explicit OTLP log endpoint, used as-is; the base endpoint never enables log export. | Unset |
LOG_TOOL_FAILURE_PAYLOADS | Log failed-call arguments and results. Redaction matches key names only; free-form values can retain secrets. | false |
LOG_TOOL_FAILURE_PAYLOAD_MAX_BYTES | UTF-8 byte cap per logged payload. | 16384 |
See .env.example for the full list of optional framework overrides.
The Dockerfile defaults to HTTP transport, stateless session mode, and logs to /var/log/browser-compat-mcp-server. OpenTelemetry peer dependencies are installed by default — build with --build-arg OTEL_ENABLED=false to omit them.
| Directory | Purpose |
|---|---|
src/index.ts | createApp() entry point — registers the tools and warms the datasets. |
src/data/ | The browserslist agent to browser-compat-data browser map. |
src/mcp-server/tools/ | Tool definitions (*.tool.ts) and the output shapes they share. |
src/services/ | bcd, baseline, targets, search, and data-version services over the bundled datasets. |
src/types/ | Ambient module declaration for caniuse-lite, which ships no types. |
tests/ | Vitest suites mirroring src/. |
docs/ | design.md — the surface, the data shapes behind it, and the decisions log. |
changelog/ | Per-version changelog files. |
The generated file tree is docs/tree.md.
See CLAUDE.md for development guidelines and architectural rules. The short version:
try/catch in tool logicctx.log for request-scoped logging, ctx.state for tenant-scoped storagesrc/index.tsIssues are welcome. Run checks and tests before submitting:
Apache-2.0 — see LICENSE for details.