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ChartAnt

by net.chartant
OverviewDiscussionsAdmin

Gauge

generate_gauge_chart
Read-onlyIdempotent

Draw a gauge (speedometer dial) for one value between a minimum and a maximum, e.g. a score of 72 out of 100. For a percentage as a filled shape use generate_liquid_chart. Returns a hosted PNG link, a share page, alt text and editable PowerPoint/Excel links.

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": {
      "value": "<value>"
    },
    "name": "generate_gauge_chart"
  }
}

Input Schema

NameRequiredDescriptionDefault
maxNoTop of the dial (default 100).
minNoBottom of the dial (default 0).
unitNoShown after the value, e.g. '%'.
themeNodefault (light) or dark background.
titleNoTitle shown above the chart.
valueYesThe value the needle points at.
widthNoImage width in pixels (default 720).
heightNoImage height in pixels (default 480).
brandThemeNoName of a brand theme saved on the user's account (their colours and footer), only when the user asks for their theme. Or "colorblind" for colours that people with colour-vision deficiency can tell apart (anyone can use it).

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observed

TDQS

A4.2/5.0
Behavior4/5

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

Annotations already declare read-only, idempotent, non-destructive, closed-world behavior, so the description only needs to add context. It does so by disclosing the outputs beyond a plain image: hosted PNG link, share page, alt text, and editable PowerPoint/Excel links, which is valuable since no output schema exists. It stops short of noting rate limits, persistence, or whether links expire.

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?

Three sentences, front-loaded with the purpose, then the sibling disambiguation, then the return values. No filler or redundancy; every sentence contributes new information.

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 single-value chart generator with full schema coverage and rich annotations, the definition covers purpose, an alternative, and the shape of the return payload. Only minor details such as link persistence or whether the returned artifacts are regenerated later are absent.

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% with per-parameter descriptions for min, max, unit, theme, title, width, height, and brandTheme, so the schema carries the semantic load. The description only adds the concrete 72-out-of-100 framing that ties value to min/max, which is marginal beyond what the schema already says.

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 and resource — "Draw a gauge (speedometer dial)" — plus the domain constraint of one value between a minimum and maximum, with a concrete example (72 out of 100). It also explicitly names the sibling generate_liquid_chart as the different tool for percentages, so an agent can distinguish them without opening schemas.

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?

Gives a clear when-to-use-elsewhere rule: for a percentage as a filled shape, use generate_liquid_chart. It does not address other plausible alternatives such as bullet charts for target-vs-actual comparisons, but the stated exclusion is concrete and actionable.

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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