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

Annotations declare readOnlyHint=false, idempotentHint=false, destructiveHint=false. The description adds genuinely new behavioral facts: append-only with no undo, and that supplying taskId triggers a real-time UI broadcast so humans see the line land. It does not mention the schema's idempotencyKey retry behavior, which is the one remaining gap.

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?

Dense and front-loaded: purpose first, then required params, then the optional broadcast behavior, then the append-only caveat. Sentences are long but each carries information; nothing is filler.

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 and six parameters, the description covers the four required fields, the mutating append-only nature, and the taskId broadcast side effect. Only the optional idempotencyKey is left entirely to the schema, which documents it fully, so this is nearly complete.

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 coverage is 100%, so the baseline is 3, but the description adds meaning beyond the schema for taskId: it explains the side effect (real-time UI broadcast) rather than just 'task this line is about.' The rest of the parameter commentary largely restates schema constraints (level <=8 chars, text <=4000 chars, monotonic lineNum).

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 states a precise verb+resource+scope: 'Append a streaming progress log line to the current agent conversation.' No sibling tool does log streaming, so an agent can identify this immediately without opening the schema.

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 framing ('streaming progress log line to the current agent conversation') and it enumerates required fields, but it never states when to choose this over siblings like create_comment or create_issue, nor any when-not condition. Adequate but leaves routing to inference.

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