event.append

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

With no annotations provided, the description carries the full burden and does so: it discloses type validation rules, the 8 KB artifact-path threshold and artifact.get follow-up, the 1 MB rejection limit, append-only behavior, the response shape, and a side effect ('test.passed may auto-checkpoint'). This is exactly the behavioral context an agent needs.

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?

Five tight sentences, front-loaded with the core action, then constraints, then return value and alternative. No filler; every clause carries actionable information.

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?

Although there is no output schema, the description supplies the return value ('{status:ok}') and the artifact indirection needed to read large payloads. For a two-parameter append tool, nothing an agent needs is missing.

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 parameter definitions are already documented; the description nonetheless adds meaning beyond the schema by giving example canonical types and size thresholds tied to payload that the schema does not mention. It stops short of describing payload merge/overwrite semantics.

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 resource ('Append one event to the current session's log') with explicit cardinality ('one event'), and explicitly contrasts with session.record for decisions/checkpoints. An agent can distinguish it from the many sibling tools 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?

Names the alternative ('To also log a decision or checkpoint use session.record') and the condition selecting it, plus states that non-canonical types are rejected. Both when-to-use and when-not-to-use are covered.

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