Metis — End Span

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

With no annotations, the description carries full burden. It discloses the computation (duration from start_ms to now) and return format. However, it does not mention side effects on a span store or error handling for invalid span_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?

Three sentences with a bullet list for args. Front-loaded purpose. No redundant information; every sentence earns its place.

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 moderate complexity and presence of output schema, the description explains return format and parameter usage. Minor gap: no mention of error handling or behavior when span_id is invalid.

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 compensate. It provides complete descriptions for all three parameters, including use of span_id from start_span(), valid status values and default, and error condition. This fully adds meaning beyond the schema.

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 'Close an open span' and 'Computes duration from start_ms to now', specifying the verb and resource. It distinguishes from siblings like 'start_span' and 'log_span' by focusing on closing and timing.

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 implies usage after 'start_span' but does not provide explicit when-to-use or when-not-to-use guidance. No alternatives are mentioned, leaving the agent to infer context from sibling tool names.

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