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ChartAnt

by net.chartant
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Bullet chart

generate_bullet_chart
Read-only

Draw a bullet chart: each measure as a bar against its target marker and range, e.g. KPIs versus goals. 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": {
      "data": "<data>"
    },
    "name": "generate_bullet_chart"
  }
}

Input Schema

NameRequiredDescriptionDefault
dataYes
themeNo
titleNoTitle shown above the chart.
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

A3.5/5.0
Behavior3/5

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

The readOnlyHint annotation already establishes this is a safe, non-mutating generation call, so the description's burden is lighter. It usefully adds that the result is an image link (no output schema exists), but says nothing about size limits, rendering latency, or what happens with malformed data.

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 short sentences, front-loaded with the action and its encoding, with zero filler. It could be marginally tighter by folding the return-value note into the first sentence, but nothing is wasted.

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 chart-rendering tool with one nested data array, the description covers the core semantics of the data, the KPI use case, and the return format. Missing details (behavior when target or max is omitted, limits on 5000 items, theme selection) are secondary and largely covered by the schema itself.

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 67%, and the description does add real meaning by explaining that each data entry becomes a bar with a target marker and a range — mapping the value/target/max fields to visual roles. It says nothing about theme, width, height, or title, though the schema documents most of those, so baseline 3 is appropriate.

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 specific verb and resource ("Draw a bullet chart") and then defines the visual encoding — measures as bars against target markers and a range — which is what actually distinguishes it from sibling generate_bar_chart or generate_gauge_chart. It stops short of explicitly naming a sibling alternative, so it lands at 4 rather than 5.

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?

"e.g. KPIs versus goals" implies the appropriate scenario, so an agent can infer when a bullet chart beats a bar chart. However, there is no explicit when-to-use/when-not-to-use guidance and no pointer to alternative tools when the user's request is ambiguous.

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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