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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safe-read behavior is covered. The description adds genuinely new behavioral context: rendering happens against LIVE data and the text payload carries the imageUrl. It stops short of covering edge cases (missing chartId, rendering failures), so a 4 rather than 5.

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?

Two sentences plus a short inline-rendering instruction; the core action and the primary use case are front-loaded. The markdown-display sentence is longer than strictly necessary but earns its place by specifying exactly how to present the result to the user.

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?

There is no output schema, so the description must explain what comes back — and it does, describing both the image return and the imageUrl in the text part. Combined with the usage and rendering guidance, an agent has everything needed to call and present the result 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%, and each parameter (chartId, sheetId, workspace) is documented in the schema itself including the workspace-token nuance. The description adds no parameter-level syntax or format detail beyond what the schema provides, so the baseline 3 applies.

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?

States a specific verb and resource — renders a sheet's pinned chart against live data and returns the image — with the scope ('one of a sheet's pinned charts') pinned down. This clearly separates it from napkin_sheets_add_chart and the other sheet tools 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.

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

Explicitly gives when to use it: 'after napkin_sheets_add_chart to confirm the chart reads well, or whenever the user asks about a chart.' It names the related sibling tool and the condition that selects this one, leaving nothing to inference.

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