io.github.cyanheads/browser-compat-mcp-server

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by cyanheads · TypeScript

Browser compatibility and Baseline status for any web feature — offline, from bundled MDN data.

io.github.cyanheads/browser-compat-mcp-server (MCP)

The io.github.cyanheads/browser-compat-mcp-server is an MCP server focused on browser compatibility and “Baseline” status for web features. It provides offline results “from bundled MDN data,” covering compatibility details for any web feature without requiring network access.

🛠️ Key Features

Browser compatibility information for web features
Baseline status tracking
Offline operation using bundled MDN data

🚀 Use Cases

Determine browser compatibility for a given web feature
Check Baseline status when planning feature support

⚡ Developer Benefits

Works offline with pre-bundled MDN data
Supports developer workflows that require compatibility and Baseline context

⚠️ Limitations

Scope is limited to data available in the bundled MDN dataset
No additional tools, endpoints, or tool behavior details are provided in the available server data

Topics

ai-agentsai-toolsbaselinebrowser-compatbrowserslistbuncaniusecyanheadsmcpmcp-servermdnmodel-context-protocolstdiostreamable-httptypescriptweb-featuresweb-platform

Captured live from the server via tools/list.

browsercompat_list_reference

Enumerate the reference vocabulary this server uses: BCD namespaces, BCD browser ids, browserslist agent ids and their BCD counterparts, Baseline states, web-features groups, and ECMAScript snapshots. Use it to build valid inputs for the other tools and to see which target browsers can be evaluated.

Parameters1

topic

string

required

Which vocabulary to list: bcd_namespaces for the 12 top-level browser-compat-data namespaces, bcd_browsers for the 17 tracked browsers, browserslist_agents for the 19 browserslist ids mapped to browser-compat-data browsers, baseline_states for the 4 Baseline states, groups for the 104 web-features groups, or snapshots for the 11 ECMAScript snapshots.

Raw schema

{
  "type": "object",
  "properties": {
    "topic": {
      "type": "string",
      "enum": [
        "bcd_namespaces",
        "bcd_browsers",
        "browserslist_agents",
        "baseline_states",
        "groups",
        "snapshots"
      ],
      "description": "Which vocabulary to list: bcd_namespaces for the 12 top-level browser-compat-data namespaces, bcd_browsers for the 17 tracked browsers, browserslist_agents for the 19 browserslist ids mapped to browser-compat-data browsers, baseline_states for the 4 Baseline states, groups for the 104 web-features groups, or snapshots for the 11 ECMAScript snapshots."
    }
  },
  "required": [
    "topic"
  ],
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "additionalProperties": false
}

browsercompat_get_feature

Get the compatibility record for one web feature: Baseline state and the date it crossed, deprecation and standards status, per-browser version added and removed with flags, vendor prefixes and partial-implementation notes, and the MDN and specification links. Accepts a BCD key such as css.selectors.has or a web-features id such as has; the response echoes which one it matched. An unresolved feature returns found: false with guidance rather than an error.

Parameters4

feature	string	required	A browser-compat-data key such as css.selectors.has, or a web-features id such as has, 1 to 200 characters. An empty or longer string is rejected against this schema; a whitespace-only string returns invalid_feature_input. Call browsercompat_search_features first if you do not already know the key.
resolve	boolean	optional	When true, a string that is neither a key nor an id falls back to the search index, such as "Container queries (size)" or "Element.prototype.animate". Its best exact matches are accepted only when they name one feature: a single key resolves to that key, several keys of one web-features feature resolve to the feature with compat_keys, and matches spanning two features are a miss. Off by default so a typo returns a miss you can correct rather than a confident answer about the wrong feature.
include_runtimes	boolean	optional	Add the bun, deno, nodejs, and oculus rows to support. Leave off for browser ship decisions.
subkeys_offset	integer	optional	Direct child keys to skip, default 0. Each subkeys page contains at most 100 keys; pass its next_offset to continue.

Raw schema

{
  "type": "object",
  "properties": {
    "feature": {
      "type": "string",
      "minLength": 1,
      "maxLength": 200,
      "description": "A browser-compat-data key such as css.selectors.has, or a web-features id such as has, 1 to 200 characters. An empty or longer string is rejected against this schema; a whitespace-only string returns invalid_feature_input. Call browsercompat_search_features first if you do not already know the key."
    },
    "resolve": {
      "default": false,
      "description": "When true, a string that is neither a key nor an id falls back to the search index, such as \"Container queries (size)\" or \"Element.prototype.animate\". Its best exact matches are accepted only when they name one feature: a single key resolves to that key, several keys of one web-features feature resolve to the feature with compat_keys, and matches spanning two features are a miss. Off by default so a typo returns a miss you can correct rather than a confident answer about the wrong feature.",
      "type": "boolean"
    },
    "include_runtimes": {
      "default": false,
      "description": "Add the bun, deno, nodejs, and oculus rows to support. Leave off for browser ship decisions.",
      "type": "boolean"
    },
    "subkeys_offset": {
      "default": 0,
      "description": "Direct child keys to skip, default 0. Each subkeys page contains at most 100 keys; pass its next_offset to continue.",
      "type": "integer",
      "minimum": 0,
      "maximum": 9007199254740991
    }
  },
  "required": [
    "feature"
  ],
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "additionalProperties": false
}

browsercompat_check_baseline

Check whether web features are safe to ship: Baseline state and the date it crossed, the browser and version that limits support, whether the feature is deprecated or discouraged, and the share of tracked global traffic that requiring it would exclude. Accepts up to 20 BCD keys or web-features ids in one call.

Parameters2

features	array	required	Up to 20 entries, each a browser-compat-data key such as css.selectors.has or a web-features id such as has, 1 to 200 characters. An empty or longer entry is rejected against this schema; a whitespace-only entry returns invalid_feature_input. Call browsercompat_search_features first for any entry whose key you do not already know.
resolve	boolean	optional	When true, an entry that is neither a key nor an id falls back to the search index, such as "Container queries (size)" or "Element.prototype.animate". Its best exact matches are accepted only when they name one feature: a single key resolves to that key, several keys of one web-features feature resolve to the feature with its feature-level Baseline and compat_keys, and matches spanning two features are a miss. Off by default so a typo returns a miss you can correct.

Raw schema

{
  "type": "object",
  "properties": {
    "features": {
      "minItems": 1,
      "maxItems": 20,
      "type": "array",
      "items": {
        "type": "string",
        "minLength": 1,
        "maxLength": 200
      },
      "description": "Up to 20 entries, each a browser-compat-data key such as css.selectors.has or a web-features id such as has, 1 to 200 characters. An empty or longer entry is rejected against this schema; a whitespace-only entry returns invalid_feature_input. Call browsercompat_search_features first for any entry whose key you do not already know."
    },
    "resolve": {
      "default": false,
      "description": "When true, an entry that is neither a key nor an id falls back to the search index, such as \"Container queries (size)\" or \"Element.prototype.animate\". Its best exact matches are accepted only when they name one feature: a single key resolves to that key, several keys of one web-features feature resolve to the feature with its feature-level Baseline and compat_keys, and matches spanning two features are a miss. Off by default so a typo returns a miss you can correct.",
      "type": "boolean"
    }
  },
  "required": [
    "features"
  ],
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "additionalProperties": false
}

browsercompat_search_features

Find web features by plain name or keyword when the canonical key is unknown, across CSS, JavaScript, HTML, Web APIs, SVG, MathML, WebAssembly, and HTTP headers. Returns ranked matches with the BCD key, the web-features id, the Baseline state, a one-line support summary, and which field matched. Feed a result key into browsercompat_get_feature for the full record.

Parameters7

query	string	required	Plain-language name, keyword, or code notation, for example "container query", "fromAsync", "Array.prototype.at", "display: grid", or "<dialog>".
namespace	string	optional	Restrict results to one top-level browser-compat-data namespace.
baseline	string	optional	Restrict results to one Baseline state.
group	string	optional	Restrict results to features in one web-features group or any group nested under it, for example "selectors" or "css". Keys with no web-features mapping never match. Call browsercompat_list_reference with topic groups for valid ids.
snapshot	string	optional	Restrict results to features in one ECMAScript snapshot, for example "ecmascript-2023". Call browsercompat_list_reference with topic snapshots for valid ids.
limit	integer	optional	Maximum results to return, from 1 to 50.
offset	integer	optional	Number of ranked matches to skip before returning results, for paging past limit. Pass the nextOffset from the previous response.

Raw schema

{
  "type": "object",
  "properties": {
    "query": {
      "type": "string",
      "minLength": 1,
      "maxLength": 100,
      "description": "Plain-language name, keyword, or code notation, for example \"container query\", \"fromAsync\", \"Array.prototype.at\", \"display: grid\", or \"<dialog>\"."
    },
    "namespace": {
      "description": "Restrict results to one top-level browser-compat-data namespace.",
      "type": "string",
      "enum": [
        "api",
        "css",
        "html",
        "http",
        "javascript",
        "manifests",
        "mathml",
        "mediatypes",
        "svg",
        "webassembly",
        "webdriver",
        "webextensions"
      ]
    },
    "baseline": {
      "description": "Restrict results to one Baseline state.",
      "type": "string",
      "enum": [
        "widely",
        "newly",
        "limited",
        "not_mapped"
      ]
    },
    "group": {
      "description": "Restrict results to features in one web-features group or any group nested under it, for example \"selectors\" or \"css\". Keys with no web-features mapping never match. Call browsercompat_list_reference with topic groups for valid ids.",
      "type": "string",
      "minLength": 1,
      "maxLength": 100
    },
    "snapshot": {
      "description": "Restrict results to features in one ECMAScript snapshot, for example \"ecmascript-2023\". Call browsercompat_list_reference with topic snapshots for valid ids.",
      "type": "string",
      "minLength": 1,
      "maxLength": 100
    },
    "limit": {
      "default": 10,
      "description": "Maximum results to return, from 1 to 50.",
      "type": "integer",
      "minimum": 1,
      "maximum": 50
    },
    "offset": {
      "default": 0,
      "description": "Number of ranked matches to skip before returning results, for paging past limit. Pass the nextOffset from the previous response.",
      "type": "integer",
      "minimum": 0,
      "maximum": 9007199254740991
    }
  },
  "required": [
    "query"
  ],
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "additionalProperties": false
}

browsercompat_compare_support

Compute whether a set of web features clears an explicit browserslist target query. Every call evaluates the whole query: each feature gets a verdict, the count of failing targets, and its own evaluated and unevaluated target counts with the share of tracked traffic each covers. The target rows behind those numbers — which release each target maps to, which targets were not evaluated and why, and the failing and unevaluated targets of each feature — cover at most ten query targets per call; page through them with target_offset and target_limit, and the verdicts, coverage, and totals stay identical on every page. A target counts as evaluated only where compatibility data was read for it, so a feature clears only when every target in the query was evaluated and supports it, and is inconclusive otherwise — a query that includes a browser with no compatibility data, as "defaults" does, never clears.

Parameters5

features	array	required	Up to 20 entries, each a browser-compat-data key such as css.selectors.has or a web-features id such as has, 1 to 200 characters. An empty or longer entry is rejected against this schema; a whitespace-only entry returns invalid_feature_input. Call browsercompat_search_features first for any entry whose key you do not already know.
targets	string	required	A browserslist query, for example "defaults" or "> 0.5%, last 2 versions", 1 to 500 characters. Required: with no query browserslist would read config from the process working directory rather than from your project.
resolve	boolean	optional	When true, an entry that is neither a key nor an id falls back to the search index, such as "Container queries (size)" or "Element.prototype.animate". Its best exact matches are accepted only when they name one feature: a single key resolves to that key and gets a verdict, several keys of one web-features feature resolve to the feature as verdict ambiguous with compat_keys, and matches spanning two features are a miss. Off by default so a typo returns a miss you can correct rather than a confident answer about the wrong feature.
target_offset	integer	optional	Zero-based position in the target list of the query at which this page of target rows starts. Pass the nextOffset of the previous response to continue. An offset at or past the number of targets returns the whole-query verdicts and totals with no target rows.
target_limit	integer	optional	How many query targets this page covers, 1 to 10. It bounds every list of target rows in the response and never the evaluation: verdicts, coverage, and totals always describe the whole query.

Raw schema

{
  "type": "object",
  "properties": {
    "features": {
      "minItems": 1,
      "maxItems": 20,
      "type": "array",
      "items": {
        "type": "string",
        "minLength": 1,
        "maxLength": 200
      },
      "description": "Up to 20 entries, each a browser-compat-data key such as css.selectors.has or a web-features id such as has, 1 to 200 characters. An empty or longer entry is rejected against this schema; a whitespace-only entry returns invalid_feature_input. Call browsercompat_search_features first for any entry whose key you do not already know."
    },
    "targets": {
      "type": "string",
      "minLength": 1,
      "maxLength": 500,
      "description": "A browserslist query, for example \"defaults\" or \"> 0.5%, last 2 versions\", 1 to 500 characters. Required: with no query browserslist would read config from the process working directory rather than from your project."
    },
    "resolve": {
      "default": false,
      "description": "When true, an entry that is neither a key nor an id falls back to the search index, such as \"Container queries (size)\" or \"Element.prototype.animate\". Its best exact matches are accepted only when they name one feature: a single key resolves to that key and gets a verdict, several keys of one web-features feature resolve to the feature as verdict ambiguous with compat_keys, and matches spanning two features are a miss. Off by default so a typo returns a miss you can correct rather than a confident answer about the wrong feature.",
      "type": "boolean"
    },
    "target_offset": {
      "default": 0,
      "description": "Zero-based position in the target list of the query at which this page of target rows starts. Pass the nextOffset of the previous response to continue. An offset at or past the number of targets returns the whole-query verdicts and totals with no target rows.",
      "type": "integer",
      "minimum": 0,
      "maximum": 9007199254740991
    },
    "target_limit": {
      "default": 10,
      "description": "How many query targets this page covers, 1 to 10. It bounds every list of target rows in the response and never the evaluation: verdicts, coverage, and totals always describe the whole query.",
      "type": "integer",
      "minimum": 1,
      "maximum": 10
    }
  },
  "required": [
    "features",
    "targets"
  ],
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "additionalProperties": false
}

README.md18 KBView on GitHub

@cyanheads/browser-compat-mcp-server

Browser compatibility and Baseline status for any web feature — offline, from MDN's browser-compat-data, web-features, and caniuse. STDIO or Streamable HTTP.

5 Tools

MCP SDK

Public Hosted Server: https://browser-compat.caseyjhand.com/mcp

Overview

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.

Tools

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: a whole-query verdict and evaluated coverage per feature, with the failing and unevaluated target rows paged ten query targets at a time.

Capability reference

`browsercompat_list_reference` _tool

Required topic: 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.
Entries carry 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` _tool

One feature, 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.
Feature-level discouraged is independent of BCD status; status.discouraged remains a compatibility alias when status exists. Unsupported and preview-only rows retain their available notes and tracking links.
limiting_browser appears only when every Baseline core browser has full, unprefixed, unflagged support at a resolvable added release.
A key with direct callable children returns subkeys: { total, keys, truncated, next_offset? }, at most 100 at a time. Continue with subkeys_offset (integer ≥0, default 0). Call one child with this tool or up to 20 with browsercompat_check_baseline; grandchildren and structural nodes are excluded.

`browsercompat_check_baseline` _tool

Up to 20 BCD keys or web-features ids, 1–200 characters each, with one result per entry in input order. A whitespace-only entry returns invalid_feature_input.
Results carry Baseline state and dates, limiting_browser under the full-support condition above, deprecated, experimental, and discouraged. usage_percent_excluded and usage_source describe the caniuse feature: a BCD key receives them only when it is the feature's sole declared compat key. Usage is absent when the scope differs or caniuse data is missing, never a fabricated zero.
all_widely_available requires every entry to resolve at widely; one miss makes it false, and it does not assess deprecation.

`browsercompat_search_features` _tool

query, 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.
Page with 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` _tool

Up to 20 features against a required targets 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.
Every call evaluates the whole query. Each verdict is clears, fails, inconclusive, miss, or ambiguous: fails when any evaluated target lacks support, clears only when every target in the query was evaluated and supports the feature, inconclusive otherwise. A query that includes a browser with no compatibility data, as defaults does, never clears. all_clear is true only when every feature clears.
A target counts as evaluated only where compatibility data was read for it. Each compared result carries failing_total, evaluated_total, evaluated_coverage_percent, unchecked_total, and unchecked_coverage_percent. The top level carries comparable_features, targets_resolved_total, evaluated_targets_total, unchecked_targets_total, and the caniuse-derived target_coverage_percent and unchecked_coverage_percent: the share covered by the targets evaluated for every compared feature, and by the rest of the query.
Target rows are paged with target_offset (integer ≥0, default 0) and target_limit (1–10, default 10). targets_resolved (the mapping inventory, each row flagged evaluated), unchecked_targets, and each result's failing_targets and unchecked_targets cover only the query targets on the page; verdicts, coverage, and totals are identical on every page. totalCount counts the targets in the query and nextOffset appears while more remain; an offset past the end returns the summaries with no rows and a notice.
failing_targets names targets with partial, prefixed, flagged, removed, unsupported, or preview_only support. unchecked_targets carries no_bcd_browser, unknown_version, no_bcd_data, or no_comparable_feature — the last when every entry was a miss or ambiguous, so nothing was compared.

Data sources

Package	Version	License	Supplies
`@mdn/browser-compat-data`	`^8.1.3`	CC0-1.0	Per-browser support, standards status, MDN and specification links
`web-features`	`^3.40.0`	Apache-2.0	Baseline state and dates, discouraged flags, groups, ECMAScript snapshots
`caniuse-lite`	`^1.0.30001812`	CC-BY-4.0	Usage weighting, plus feature titles for the search index
`browserslist`	`^4.29.1`	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 ~97.3% of global traffic caniuse tracks. Full license texts and notices are in THIRD_PARTY_NOTICES.md.

Features

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:

All four datasets are bundled and loaded in process — no runtime network calls, no API key, no rate limit, and nothing to configure
Baseline is read per browser-compat-data key from status.by_compat_key, never rolled up from the feature level, because keys under one feature legitimately disagree
One shared resolver behind every tool: exact BCD key, then web-features id, then a moved redirect, and only under resolve: true the search index's best exact matches, when they name one feature
Target versions are ordered by browser-compat-data's release index rather than parsed version strings, with the caniuse spellings normalized both directions (safari 16.0 ↔ 16, samsung 20 ↔ 20.0)

Agent-friendly output:

Every response echoes data_version — the version of each bundled dataset behind the answer, since a pinned snapshot goes stale on exactly the newest features
A pass is never claimed for a browser that was not evaluated: a feature clears a target query only when compatibility data was read for every target in it, and a target without data is reported in unchecked_targets and makes the verdict inconclusive
Misses are results, not failures — found: false with guidance naming the next call, and typed error reasons carrying recovery hints for the input a caller has to fix
Usage figures state the population they are a share of, and carry the caniuse attribution on every response that reports one
BCD markup becomes plain text with anchor labels and URLs preserved. Markdown renders literal names such as <dialog> visibly; structured text keeps the original plain-text element names.

Getting started

Public Hosted Instance

A public instance is available at https://browser-compat.caseyjhand.com/mcp — no installation required. Point any MCP client at it via Streamable HTTP:

json

{
  "mcpServers": {
    "browser-compat-mcp-server": {
      "type": "streamable-http",
      "url": "https://browser-compat.caseyjhand.com/mcp"
    }
  }
}

Self-Hosted / Local

Add the following to your MCP client configuration file:

json

{
  "mcpServers": {
    "browser-compat-mcp-server": {
      "type": "stdio",
      "command": "bunx",
      "args": ["@cyanheads/browser-compat-mcp-server@latest"],
      "env": {
        "MCP_TRANSPORT_TYPE": "stdio",
        "MCP_LOG_LEVEL": "info"
      }
    }
  }
}

Or with npx (no Bun required):

json

{
  "mcpServers": {
    "browser-compat-mcp-server": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@cyanheads/browser-compat-mcp-server@latest"],
      "env": {
        "MCP_TRANSPORT_TYPE": "stdio",
        "MCP_LOG_LEVEL": "info"
      }
    }
  }
}

Or with Docker:

json

{
  "mcpServers": {
    "browser-compat-mcp-server": {
      "type": "stdio",
      "command": "docker",
      "args": [
        "run", "-i", "--rm",
        "-e", "MCP_TRANSPORT_TYPE=stdio",
        "ghcr.io/cyanheads/browser-compat-mcp-server:latest"
      ]
    }
  }
}

For Streamable HTTP, set the transport and start the server:

MCP_TRANSPORT_TYPE=http MCP_HTTP_PORT=3010 bun run start:http
# Server listens at http://localhost:3010/mcp

Prerequisites

Bun v1.4.0 or higher (or Node.js v24+).
No API keys, accounts, or network access required — every dataset ships with the package.

Installation

Clone the repository:

git clone https://github.com/cyanheads/browser-compat-mcp-server.git

Navigate into the directory:

cd browser-compat-mcp-server

Install dependencies:

bun install

Configure environment (optional):

cp .env.example .env
# edit .env if you want to override transport or logging defaults

Configuration

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.

Running the server

Local development

# One-time build
bun run rebuild

# Run the built server
bun run start:stdio
# or
bun run start:http

bun run devcheck   # Lint, format, typecheck, security
bun run test       # Vitest test suite
bun run lint:mcp   # Validate MCP definitions against spec

Docker

docker build -t browser-compat-mcp-server .
docker run --rm -p 3010:3010 browser-compat-mcp-server

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.

Project structure

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.

Development guide

See CLAUDE.md for development guidelines and architectural rules. The short version:

Handlers throw, framework catches — no try/catch in tool logic
Use ctx.log for request-scoped logging, ctx.state for tenant-scoped storage
Register new tools directly in src/index.ts
Data integrity: read the bundled datasets as they are and preserve their uncertainty; never fabricate a support fact the data does not carry

Contributing

Issues are welcome. Run checks and tests before submitting:

bun run devcheck
bun run test

License

Apache-2.0 — see LICENSE for details.

Install

Tools (5)

browsercompat_list_referencebrowsercompat_get_featurebrowsercompat_check_baselinebrowsercompat_search_featuresbrowsercompat_compare_support

Configuration

Environment variables

MCP_LOG_LEVELdefault info

Sets the minimum log level for output (e.g., 'debug', 'info', 'warn').

MCP_HTTP_HOSTdefault 127.0.0.1

The hostname for the HTTP server.

MCP_HTTP_PORTdefault 3010

The port to run the HTTP server on.

MCP_HTTP_ENDPOINT_PATHdefault /mcp

The endpoint path for the MCP server.

MCP_AUTH_MODEdefault none

Authentication mode to use: 'none', 'jwt', or 'oauth'.

Add to VS Code Add to Cursor

claude_desktop_config.json

json

{
  "mcpServers": {
    "browser-compat-mcp-server": {
      "command": "npx",
      "args": [
        "-y",
        "@cyanheads/browser-compat-mcp-server@0.2.0",
        "run",
        "start:stdio"
      ],
      "env": {
        "MCP_LOG_LEVEL": "info"
      }
    }
  }
}

io.github.cyanheads/browser-compat-mcp-server (MCP)

🛠️ Key Features

🚀 Use Cases

⚡ Developer Benefits

⚠️ Limitations

Topics

browsercompat_list_reference

browsercompat_get_feature

browsercompat_check_baseline

browsercompat_search_features

browsercompat_compare_support

@cyanheads/browser-compat-mcp-server

Overview

Tools

Capability reference

browsercompat_list_reference tool

browsercompat_get_feature tool

browsercompat_check_baseline tool

browsercompat_search_features tool

browsercompat_compare_support tool

Data sources

Features

Getting started

Public Hosted Instance

Self-Hosted / Local

Prerequisites

Installation

Configuration

Running the server

Local development

Docker

Project structure

Development guide

Contributing

License

Install

Configuration

Related servers

`browsercompat_list_reference` _tool

`browsercompat_get_feature` _tool

`browsercompat_check_baseline` _tool

`browsercompat_search_features` _tool

`browsercompat_compare_support` _tool