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

Annotations already declare readOnlyHint=false and destructiveHint=true, so the write nature is structured. The description adds genuinely new context beyond that: every connected subscriber receives the message in real time, it is an outward-facing side effect, and the REST equivalent endpoint. It does not cover error behavior or delivery semantics failures.

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 short sentences, front-loaded with the WRITE classification, then the effect, then the caution. No filler; each 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?

For a four-parameter write tool with full schema coverage and no output schema, the description covers purpose, effect, and a pre-call caution. Missing only edge-case behavior (e.g., failure modes, whether the call blocks on delivery), which keeps it short of a 5.

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 all four parameters (data, name, channel, clientId) are already documented in the schema with examples. The description adds no parameter-level meaning, so the baseline of 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 (publish) and resource (message to a channel), explicitly labeled WRITE. This clearly separates it from the sibling read tools like ably_get_channel_history or ably_list_channels.

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?

Gives a clear usage condition ('confirm the channel and payload before calling') and frames it as an outward-facing side effect. It does not name an alternative tool, but the sibling set is entirely read-only, so the routing decision is unambiguous.

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