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ChartAnt

by net.chartant
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Gauge

generate_gauge_chart
Read-only

Draw a gauge (speedometer dial) for one value against a maximum, e.g. 72 of 100 or a score. Returns an image link.

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
maxNo
minNo
unitNo
themeNo
titleNoTitle shown above the chart.
valueYes
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

B3.2/5.0
Behavior3/5

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

readOnlyHint=true already establishes this is a safe, non-mutating render, so the bar is lower. The description adds genuine value with "Returns an image link," which the annotations do not cover, but says nothing about theme/brandTheme behavior, whether images are persisted, or any limits.

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?

Two compact sentences with the visual form and the return value front-loaded; nothing is wasted. It could have spent the saved space on the unmentioned parameters, which is the only structural shortfall.

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

Completeness3/5

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

For a 9-parameter chart generator with 44% schema coverage and no output schema, the description covers purpose and return type but leaves most rendering parameters unexplained. Adequate to invoke the simplest call (value only), not adequate to use it well.

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

Parameters2/5

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

Schema description coverage is 44%, below the point where the schema carries the load, so the description should compensate — it only gestures at value and max. It says nothing about min (implied range floor), unit, theme, title, width/height, or the brandTheme account dependency.

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

Purpose4/5

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

States a concrete verb+resource pair ("Draw a gauge / speedometer dial") and defines the data shape as one value against a maximum with an example (72 of 100). That is enough to distinguish it from the time-series and multi-category siblings, though it never names an alternative for comparison.

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

Usage Guidelines3/5

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

The phrase "for one value against a maximum" implicitly tells the agent when this chart fits, but no explicit when-not guidance or sibling routing is given (e.g., a bullet chart for target comparison or a liquid chart for a bare percentage). Usage is inferable but not directed.

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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