snapdiff-mcp

snapdiff_capture_baseline

Capture a baseline screenshot of a page to serve as the reference for visual change verification. Use this once per page before verifying UI changes.

Instructions

Capture the current state of a page as the visual baseline for a SnapDiff project. Call this once per page before using snapdiff_verify_ui_change — the baseline is the reference screenshot that all future verifications diff against.

For localhost URLs, the page is captured locally with a headless browser (no tunnel needed). For public URLs, the SnapDiff backend captures it. Returns when the baseline is confirmed in place.

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": {
      "project": "<project>",
      "page_name": "<page_name>",
      "url": "<url>"
    },
    "name": "snapdiff_capture_baseline"
  }
}

Input Schema

Name	Required	Description
`project`	Yes	Project slug or ID (prj_xxx).
`page_name`	Yes	Page name within the project (e.g. "account", "homepage"). Used to match this baseline when verifying.
`url`	Yes	URL of the page to capture as the baseline. Localhost URLs are captured locally — no tunnel required.
`branch`	No	Branch to store the baseline on. Defaults to the project's default branch.

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.4.2Jun 17, 2026

TDQS

A4.4/5.0

Behavior3/5

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

No annotations provided; description carries full burden. It mentions that baseline is a reference screenshot and that the tool returns when confirmed, but does not disclose if calling multiple times overwrites the baseline or potential side effects. Adequate but not thorough.

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

Conciseness5/5

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

Four concise sentences with front-loaded purpose. No redundant information; every sentence adds value.

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

Completeness4/5

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

All 4 parameters are described in schema, and description adds context for two of them. No output schema, but description mentions return behavior. Adequate for a tool with moderate complexity.

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

Parameters4/5

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

Schema coverage is 100%, and description adds extra meaning: explains that 'url' parameter for localhost does not require a tunnel, and 'page_name' is used to match during verification. Exceeds baseline of 3.

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?

Description clearly states the tool's purpose: capture current page state as a visual baseline for SnapDiff. It distinguishes from sibling tools like snapdiff_verify_ui_change by explaining it is a prerequisite.

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

Usage Guidelines5/5

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

Explicitly says 'Call this once per page before using snapdiff_verify_ui_change' and explains difference between localhost and public URLs, giving clear guidance on when to use this tool.

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

Deploy Server