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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false; the description adds that nothing is created and, importantly, that failures come back as per-channel issues like media_required or text_too_long rather than an exception. It does not say what happens for an unknown channel id or a malformed 'when' value, which is the remaining behavioral gap.

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 sentences, zero filler. The scope constraint and the return contract are both front-loaded where the agent needs them.

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 read-only validator with a fully documented schema and no output schema, the description supplies exactly what is missing: that it is non-mutating and what the response looks like on success and failure.

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 the schema already explains text, channels, when and mediaIds, including per-channel overrides. The description merely echoes the parameter names in validation terms and adds no format or syntax detail beyond that baseline.

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?

Specific verb plus resource: 'Check the text, channels, media and time against every channel's rules'. The clause 'without creating anything' separates it from create_post, so an agent can distinguish the validator from the writer without opening either 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?

The title plus the phrase 'without creating anything' make the intended workflow clear: validate before creating. It stops short of naming create_post as the follow-up step or stating when validation can be skipped, so the alternative is implied rather than explicit.

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