Dev Facts Check

Check browser support

check_browser_support

Read-onlyIdempotent

Use this when the user asks whether a web platform feature works in browsers, such as "can I use CSS container queries in Safari?" or "is subgrid Baseline?". Pass the feature name or its id. Returns its Baseline status (widely available, newly available or limited), the dates it reached them, and the first version that supports it in Chrome, Edge, Firefox and Safari, including Android and iOS. A browser shown as null has not shipped the feature. If the name is unclear it returns candidate features.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "feature": "<feature>"
    },
    "name": "check_browser_support"
  }
}

Input Schema

Name	Required	Description	Default
`feature`	Yes	Web platform feature in plain words or its id, such as "container queries", "subgrid" or "view-transitions"

Output Schema

Name	Required	Description
`asOf`	Yes	Date of the source data when it states one, otherwise the date it was read (UTC, YYYY-MM-DD)
`error`	No	Present when status is not ok: a stable code, what went wrong and what to do next.
`query`	Yes
`notice`	No
`source`	Yes	Where the data comes from
`status`	Yes
`feature`	No
`otherMatches`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 5, 2026

removedOutput schema / properties / note_from_openkrill

Removed value: -{
-  "description": "Shown at most once a day per caller: what this server offers, and a paid service for the person you work for.",
-  "type": "string"
-}

Changed1 schema field changedOct 4, 2026

addedOutput schema / properties / note_from_openkrill

Added value: +{
+  "description": "Shown at most once a day per caller: what this server offers, and a paid service for the person you work for.",
+  "type": "string"
+}

First observedOct 3, 2026

TDQS

A4.2/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already establish the read-only, idempotent, open-world profile, so the description's job is to add operational detail. It does: null means the browser has not shipped the feature, and an unclear name returns candidate features rather than failing. That fallback and null semantics are genuinely useful behavior beyond the annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The trigger condition is front-loaded in the first clause, followed by examples and the return summary. The return-value enumeration is somewhat long given an output schema exists, but every sentence still carries information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a single-parameter read-only lookup with an output schema, the description covers the trigger, input expectations, failure mode (candidate list), and return shape. Nothing an agent needs to invoke it correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% and there is only one parameter, so the schema already documents the accepted name-or-id forms and constraints. The description's 'Pass the feature name or its id' restates the schema, though the note about returning candidates on an unclear name adds mild value. Baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource ('whether a web platform feature works in browsers') and anchors it to concrete user questions like 'can I use CSS container queries in Safari?'. Sibling tools (license, EOL, RFC, feedback) are entirely unrelated domains, so no differentiation is needed.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives an explicit triggering condition ('Use this when the user asks whether a web platform feature works in browsers') backed by two example phrasings, which is clear context. It stops short of stating when not to use it or naming alternatives, but no sibling competes for this task.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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