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

Annotations only declare readOnlyHint=false, so the description carries most of the behavioral burden. The 'Base64 bytes → Storage → message-send' pipeline is genuinely useful — it tells the agent this is a two-stage upload-then-post operation with a storage dependency. However, it says nothing about permission requirements, whether a failed storage step leaves orphans, or whether posting is idempotent/retryable.

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 clauses, zero filler, and the core action is front-loaded before the pipeline detail. Every word earns its place, with no repetition of schema facts beyond what clarifies the mechanism.

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 7-parameter mutation with no output schema, the definition covers what the tool does and the underlying mechanism, which is a reasonable baseline. The remaining gaps — return value (message id vs storage ref), permission requirements, and the space_id/channel_id distinction — are real but modest given the schema already documents size limits and encoding.

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 71%: mime, filename, channel_id and file_base64 are described in the schema, but caption, space_id and reply_to_id are documented nowhere. The description adds no parameter meaning beyond restating that bytes are base64 — notably it never clarifies the space_id vs channel_id relationship, which is the genuinely ambiguous parameter here.

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 (send), resource (a FILE), and target (a persistent channel), plus the result type ('first-class `file` message'). It implicitly separates itself from plain text sends like mIRC_post_message, but never names the closely related mDM_send_file or mIRC_send_edge, so sibling differentiation is only partial.

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 when-to-use guidance at all — nothing says when to choose this over mIRC_post_message, mIRC_send_edge, mIRC_send_voice, or mDM_send_file, nor what prerequisites (channel membership, token) are required. The agent must infer the selection rule from the tool name alone.

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