Add chart event marker

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

Annotations include readOnlyHint=false, destructiveHint=false, and idempotentHint=false, which already convey that this is a mutating, non-idempotent operation. The description adds the 'replace' behavior, but does not elaborate on side effects (e.g., whether an existing marker with the same id is replaced) or any state changes beyond that. Since annotations are present, the description adds moderate extra context but does not fully disclose behavior like does not clarify if replace is keyed by id.

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 a single, concise sentence that is front-loaded with the action ('Add or replace a marker') and immediately lists the event types. Every word adds value, with no filler or redundant phrasing.

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 tool has 6 parameters, no output schema, and no parameter descriptions in the schema, the description is critically incomplete. It does not explain the format for 'time' (number vs string), how 'replace' works with the 'id' parameter, or the semantics of 'position' relative to bars. The description fails to provide enough context for the agent to correctly invoke the tool, especially given the low schema coverage.

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?

The schema has 0% description coverage, meaning the description must explain the parameters. However, the description only mentions event types ('SQ, signal confirmation, participant-flow events, or scenario triggers') but does not map them to specific parameters. None of the six properties (id, text, time, color, shape, position) are explained in the description, leaving the agent to infer meaning only from the schema's type/enum/default constraints, which is insufficient.

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 clearly states the tool's action: 'Add or replace a marker' and specifies the resource: a chart marker for specific event types (SQ, signal confirmation, participant-flow events, or scenario triggers). This distinguishes it from sibling tools like chart_remove_marker or chart_add_indicator, making the purpose explicit and specific.

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 indicates the tool is for adding or replacing certain types of markers, but it does not explicitly state when to use this tool versus alternatives (e.g., chart_add_indicator, chart_add_level). No guidance is given on prerequisites or exclusions, leaving the usage context only implied by the marker-specific terminology.

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