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

Annotations already declare readOnlyHint=true and destructiveHint=false, so 'Nothing is changed' is largely redundant. The description earns credit for beyond-annotation behavior: rows are permission-scoped ('as you may see them'), non-chart widgets are rejected, and the diagnostics cover specific failure modes (missing columns, empty marks, alphabetical bars, overlapping text).

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?

Roughly three sentences, front-loaded with the core action and with zero filler. The phrasing 'from its rows as you may see them' is slightly convoluted but is doing real work (permission scoping), so nothing is truly wasted.

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 carries the burden of describing returns, and it does so concretely: an image, the visible rows, a row count, plus a conditional diagnostics list for Vega-Lite. What is missing is any hint about size, pagination, or how many rows come back, which matters for an image-returning tool.

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 coverage is 100%, and both parameters are already documented in the schema with their provenance (fastero_list_reports, fastero_get_dashboard, fastero_list_projects). The description adds no further semantics about reportId or projectId, 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?

The description names a specific action (render a saved chart as an image) plus concrete outputs: the picture, the rows, the row count, and a Vega-Lite lint report. That is far more specific than the title 'Show report'. It does not, however, distinguish itself from the close siblings fastero_get_report or fastero_show_chart, which an agent must otherwise infer.

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?

It explicitly routes mutation intent away ('To change the chart, fastero_update_report') and states a when-not case ('A widget that is not a chart is refused'), which prevents a predictable failure. The remaining gap is that the read-side alternatives (fastero_get_report for metadata, fastero_show_chart) are never contrasted.

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