pin_message

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

Annotations already declare openWorldHint, idempotentHint, and non-destructive, so the bar is lower. The description still adds real context beyond them: the pin is publicly visible to all participants, the call contacts Signal's servers, and re-pinning is a no-op (restating idempotency in plain terms). Only the return shape and any auth/rate-limit caveats are left implicit.

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?

Front-loaded with the core action and visibility caveat before the routing advice and parameter notes; every sentence carries information. It is dense as a single block, and the parameter guidance is interleaved with usage guidance rather than separated, which slightly hurts scannability.

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 4-parameter mutation with no output schema, the description covers the missing return contract ('Returns {status: \'message pinned\'}'), the visibility consequence, the idempotent behavior, and both conversation-targeting modes. An agent has everything needed to call it correctly.

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 baseline is 3, but the description adds format meaning the schema lacks: E.164 for target_author, millisecond timestamp, and the provenance of the value ('message id in get_conversation'). It also restates the recipient/group_id mutual-exclusivity in prose. It does not, however, clarify failure modes for ambiguous or mismatched identifiers.

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 (pin) and resource (message) with explicit scope: at the top of a DM or group conversation, visible to all participants. It actively distinguishes itself from two siblings by name (send_note_to_self for private bookmarks, unpin_message for removal), so an agent can route correctly without opening any 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?

Explicit when-not guidance ('don't use it as a private bookmark — send_note_to_self instead') plus the inverse operation (unpin_message) and the recipient-vs-group_id selection rule including the 'neither is an error' edge case. Nothing about tool selection is left to inference.

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