agent_receive_messages

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

With no annotations, the description carries the full burden and delivers: relay-side decryption, read-marking side effect visible to senders, up-to-50 relay-ordered default, skipped_unreadable handling, the malformed-message blocking risk, the env-var gate, the lack of end-to-end encryption, and an untrusted-content warning. This is unusually rich disclosure of non-obvious behavior.

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?

Purpose is front-loaded and each sentence carries distinct operational information (side effects, gating, failure modes, security posture). It is dense and somewhat long, but nearly every clause earns its place rather than padding.

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, so return-value explanation is unnecessary, and the description still covers behavior, side effects, constraints, failure modes, and security caveats thoroughly. Nothing an agent needs in order to call this correctly 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 the baseline is 3, but the description adds meaning beyond it by stating the default return behavior ('oldest unread messages, up to 50, in relay order') and that the model does not choose which messages are marked. It also notes the env-var refusal condition, though the schema already documents that. The stated 50-message page differs from the schema's max of 100, worth noting as a minor ambiguity.

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 ('Read the inbox of this machine's relay identity') and immediately distinguishes itself from siblings like agent_read_channel and agent_mark_read by describing relay-side decryption and the read-marking side effect. An agent can tell what this tool does 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?

Gives clear operating guidance: 'Call it with no arguments', and explains exactly when since/limit are permitted (only under VOIDLY_MCP_RELAY_ALLOW_STATE_CHANGES=1). It does not explicitly name alternative siblings such as agent_unread_count or agent_mark_read_batch, but the constraint on which messages get marked provides strong context for choosing this path.

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