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

The description is unusually candid that 'the first signal of a new name creates its monitor' — a state-creating side effect — but annotations declare readOnlyHint: true, which directly conflicts with that disclosure. It also says nothing about what the call returns or what happens on rate limits/auth failure, leaving the agent to reconcile a mutation story against a read-only annotation.

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?

The routing rationale is front-loaded and useful, but 'the first signal of a new name creates its monitor' is stated twice in a four-sentence description, and the closing sentence largely repeats the second. There is real waste for a three-parameter tool.

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 simple signal-emitting tool with no output schema, the description covers the routing model, the monitor auto-creation rule, and inherited settings, which is enough to call it correctly. The only gap is what the response contains on success or 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 coverage is 100%, so slug, signal and ingestKey already carry descriptions. The prose restates them (name becomes the monitor name; start/fail/exit code) and adds only the contextual note that `cron`, `tz` and `grace_sec` inherit from the plain ping-by-name — marginal added value over the schema, which fits the baseline 3.

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?

The description names a specific verb and resource ('Send start, fail or an exit code by name, with the ingest key') and distinguishes this from the id-keyed routes by explicitly equating it to `/in/:id/start`, `/in/:id/fail` and `/in/:id/:exit_code`. It effectively separates itself from signal_start/signal_fail/signal_exit_code (id-based) without naming the sibling tools directly, which keeps it at a 4.

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?

It states the selecting condition plainly: 'for a fleet that only knows the ingest key: the job sends its name, not the monitor id.' That tells an agent when this is the right choice versus the id-based siblings. It never states a when-not or names an explicit alternative, so it stops short of a 5.

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