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

With no annotations, the description carries the burden alone. 'History is never mutated' is a genuinely useful disclosure of the append-only, non-destructive semantics that an agent could not infer elsewhere. It omits permissions, whether the stream must pre-exist, and the fact that several event-type prefixes are rejected server-side (only in schema).

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 short sentences, neither wasted: the first states the action, the second states the invariant. Purpose is front-loaded and there is no 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?

An output schema exists and the schema fully documents all 7 parameters, so the description needn't cover return values or field syntax. What remains missing for a 7-param write tool with zero annotations is routing guidance versus event_list and any precondition or failure-mode note.

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% and every parameter (stream_id formats, event type naming rules, actor ignored, payload corrections) is documented in the schema itself. The description adds no parameter-level meaning beyond that, so the baseline 3 applies.

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 (append) and resource (one event to a stream), which immediately distinguishes it from the read-side sibling event_list. It stops short of explicitly naming that sibling or the adjacent write tools, so differentiation is implied rather than stated.

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?

There is no explicit when-to-use guidance: nothing says to prefer event_list for reading, nor what preconditions exist (must the stream already exist? are there event-type restrictions?). The immutability note hints at a correction workflow (append rather than modify) but only in the schema's payload text, not the description.

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