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

readOnlyHint=true already establishes this is a safe read, so the description adds the useful fact that the response includes the span's own logs and attributes. It does not disclose error behavior (missing run/span), pagination, or trace-size limits, but the annotation carries the main safety burden.

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?

Two tight sentences with the verb and resource front-loaded and no filler. The endpoint line is mildly redundant with the name but compact and useful for API-oriented agents, so it 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?

With no output schema, the description carries the return-value burden and only partially discharges it ('logs and attributes' hints at shape without structure). For a simple two-param read tool backed by a readOnly annotation this is adequate but leaves the response format under-specified.

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 both run_id and span_id are already documented in the schema; baseline 3 applies. The endpoint template shows them as path parameters, but the description adds no format or sourcing detail 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?

Names a specific verb+resource ('Fetch a single span from a run's trace') and adds scope detail (its own logs and attributes). It distinguishes span-level retrieval from the broader run and trace siblings implicitly, but never names them, so an agent must infer the difference from trigger_get_run_trace/trigger_get_run.

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?

Usage is implied by the scoping phrase 'a single span from a run's trace' – you reach for this when you need one span rather than the whole trace. However, no when-to-use condition, prerequisites, or alternative (get_run_trace) is stated explicitly.

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