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ChartAnt

by net.chartant
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Bullet chart

generate_bullet_chart
Read-onlyIdempotent

Draw a bullet chart: each measure as a bar against its target marker, e.g. KPIs versus goals. For headline numbers with changes use generate_kpi_card. 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": {
      "data": "<data>"
    },
    "name": "generate_bullet_chart"
  }
}

Input Schema

NameRequiredDescriptionDefault
dataYesOne row per measure: {category, value, target?, max?}.
themeNodefault (light) or dark background.
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

A3.9/5.0
Behavior3/5

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description's remaining job is output shape, and it does list PNG link, share page, alt text and editable PowerPoint/Excel links. It says nothing about latency, row limits for the 5000-row cap, or error behavior, so it adds useful but not deep context.

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?

Three short sentences, front-loaded with the visual definition, then the alternative, then the return values - nothing redundant. The output list is slightly packed but each item is distinct information an agent would otherwise lack.

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?

With no output schema, the description correctly spends its budget enumerating return artifacts, and the input schema carries all six parameters with enums and bounds. Missing only operational details like generation time or what happens with malformed rows, which are minor for a read-only chart generator.

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 description coverage is 100%, so every parameter is already documented, establishing a baseline of 3. The description's 'measure as a bar against its target marker' clarifies the intended category/value/target data shape but adds no format or default detail beyond the schema.

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?

Specific verb+resource ('Draw a bullet chart') with a concrete rendering rule ('each measure as a bar against its target marker') and a domain example ('KPIs versus goals'). It explicitly names the sibling it contrasts with (generate_kpi_card), so an agent can distinguish it without opening a schema.

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?

Explicitly routes headline-number-with-change cases to generate_kpi_card, which is a clear when-not-to-use signal. It stops short of disambiguating against other measure-comparison siblings such as generate_bar_chart or generate_gauge_chart, so guidance is clear but not exhaustive.

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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