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webability

by io.github.snayyar00
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Check color contrast

check_color_contrast
Read-onlyIdempotent

Check a foreground/background color pair against WCAG contrast thresholds. When it fails, suggests BRAND-aligned replacements — extracts the actual brand palette from a live URL using our scanner (CSS vars + most-used colors), or use a provided brandColors array. No url and no brandColors = ratio + pass/fail only. 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.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
urlNoLive URL to extract brand palette from (uses our scanner — CSS vars + dominant colors).
isBoldNoWhether text is bold (default false)
contextYesExplain 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."
fontSizeNoFont size in px (default 16)
llm_modelYesThe 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.
backgroundYesBackground color (hex or rgb)
foregroundYesForeground color (hex or rgb)
brandColorsNoPre-supplied brand palette. Skips URL extraction if provided.
tunnel_secretNoSecret printed by `webability-tunnel`. Required when `url` is a tunnel URL; the URL alone will be refused by the relay. Ignored otherwise.
conversation_idNoEcho the conversation_id from the server's previous response. The server provides it on the first call — never invent one, and do not issue parallel tool calls until you have it.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observed

TDQS

A4.7/5.0
Behavior5/5

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

Annotations only tell the agent this is a safe, idempotent, open-world read. The description adds non-obvious runtime behavior: it runs in a hosted cloud environment that cannot reach the caller's machine, private/localhost addresses are refused, and tunnel URLs are rejected unless accompanied by the relay secret. That is exactly the kind of context annotations cannot carry.

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?

Front-loaded with the core purpose, then conditions, then the hosting caveat. Dense but every clause carries information; the localhost/tunnel paragraph is long relative to the rest, though it is load-bearing for correctness of calls.

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?

For a 10-parameter, open-world tool with no output schema, the description covers the tricky call-shaping decisions (palette sourcing, private-address refusal, tunnel secret) and hints at returns ('ratio + pass/fail only', 'suggests BRAND-aligned replacements'). Minor gap: the shape of the suggested replacements isn't described, though the agent can discover it from the response.

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 description coverage is 100%, so baseline is 3. The description earns above baseline by explaining the interaction semantics the schema states only locally: `url` vs. `brandColors` are alternatives, omitting both degrades output to ratio + pass/fail, and `tunnel_secret` is conditionally required (ignored otherwise).

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?

States a specific verb (check) and resource (foreground/background color pair) against a named standard (WCAG contrast thresholds), and goes on to distinguish its brand-replacement mode from its bare ratio mode. No sibling tool (scan_page, visual_audit, check_aria) does this, so the agent can route to it unambiguously.

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 covers the branch conditions: 'No `url` and no `brandColors` = ratio + pass/fail only', and URL extraction vs. pre-supplied palette. It also names the exclusion ('localhost and private addresses are refused') and gives two concrete alternatives for local dev (run MCP locally, or tunnel with `tunnel_secret`).

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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