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

readOnlyHint=true already tells the agent this is a safe read. The description adds value beyond that by disclosing the data source ('stats artifacts') and the return shape ('points + Vega-Lite spec'), which is genuinely useful. It omits behavior for missing artifacts and any note about the limit cap on returned points.

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?

One dense sentence with no filler, and the core output (points + Vega-Lite spec) is placed last where it is easy to find. It stays compact rather than padding with restated schema details.

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's note about points plus a Vega-Lite spec usefully covers the return value. For a 3-parameter tool at 0% schema coverage, though, an agent still lacks guidance on the limit parameter and on failure modes when stats artifacts are unavailable.

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 0%, so the description must carry parameter meaning and largely doesn't. It echoes the four series enum values, which the schema already enumerates, but never explains backtestId's role or the limit parameter's default/max (1000/5000) and how it caps points returned.

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?

Specific verb ('Builds chart-ready time series data') plus resource, and it enumerates the exact series types that the tool handles, so the agent knows this is the chart-data endpoint rather than a raw artifact fetch. It does not explicitly contrast itself with close siblings such as get_backtest_visuals or show_backtest_dashboard, so it stops short of 5.

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 phrase 'chart-ready' implies the charting use case, but there is no statement of when to pick this over get_backtest_visuals, get_portfolio_series, or get_backtest_artifact. No preconditions (e.g. a completed backtest with stats artifacts present) are given.

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