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

No annotations are supplied, so the description carries the full behavioral burden. It does add substantive content rules — never fabricate factual dates or durations, disclose relative timing as estimated, use ordinal phases for undated processes — plus a soft event-count range and default layout. However, it says nothing about persistence, what is returned on creation (chart ID, share link), or how the created chart relates to edit_chart/get_chart, which an agent needs for a create-type tool with zero annotation coverage.

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?

Four short sentences, front-loaded with the purpose and use cases before the content rules. Dense but every sentence carries a constraint; minor overlap with the schema's own date-format guidance keeps it from being maximally tight.

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?

For a nested-array creation tool with no output schema and no annotations, the description covers input quality rules well but omits post-creation behavior and any sibling differentiation. An agent knows how to build the payload but not what it gets back or when to prefer another chart type.

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 the schema already documents every parameter including date formats, era grouping, and the key-marker rule. The description reinforces the event marker requirement and era grouping conceptually, but adds no format or constraint detail beyond what the schema states, so 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 artifact ('Create a timeline of events in chronological order') and immediately names concrete scenarios (roadmaps, company history, sprint/release schedules). An agent can distinguish this from create_lifecycle_chart or create_flowchart by the chronological ordering emphasis.

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 parenthetical use cases give clear positive guidance on when this tool fits, and the 'marker' rule tells the agent what input shape qualifies. It stops short of naming alternatives or exclusion cases (e.g., use create_lifecycle_chart for stages rather than a timeline), so it is clear but not routing-complete.

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