export_chart

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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is covered. The description adds meaningful behavioral context: it requires the environment variable BLUEPRINT_CHART_EDITOR_URL, states that preview failures never block the export, and explains the availability of urls.{png,svg,bpc} based on MCP_PUBLIC_URL. This goes beyond the annotations and enriches the agent's understanding.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is moderately concise, with three sentences that pack substantial detail: the main purpose, the return object structure with per-field explanations, environment requirements, and failure handling. Every sentence contributes to the overall understanding, though the enumeration of URL fields makes it slightly denser than necessary. It is well-structured and front-loaded with the core behavior.

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

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

Given the presence of an output schema and only two simple parameters, the description covers the essential context: return value semantics, environment prerequisites, failure behavior, and a timeout-related tweak (modelVisible). It does not explicitly state what happens on invalid input, but that is a minor gap given the tool's purpose and the fact that the schema already describes the source as 'validated.' Overall, it is comprehensive enough for an agent to select and invoke correctly.

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

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

Schema description coverage is 100%, so both parameters are already well-documented. The tool description does not add significant additional meaning beyond what the schema provides; it mostly echoes the schema's descriptions. The explanation of modelVisible in the description is nearly identical to the schema description. Therefore, baseline 3 is appropriate.

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

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

The description opens with a specific verb+resource: 'Turn a validated .bpc source into shareable URLs plus an inline visual preview.' This clearly distinguishes it from sibling tools like render or validate_dsl, which focus on other aspects. It explains exactly what is produced (URLs, preview) and the use case (before sharing).

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

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

The description provides clear context for when to use the tool: when you have a validated .bpc source and want shareable URLs/preview. It implies the tool is for sharing, but it does not explicitly contrast with alternatives like render or list_chart_types, nor does it state when not to use it. Hence a 4, not a 5.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.