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

Beyond the annotations, the description discloses key side effects: the message is persisted, and the agent execution resumes if the run is completed/interrupted and has no pending human request. It also documents a specific failure mode, HTTP 410 with code sandbox_expired when workspace data retention has deleted answers. This is meaningful behavioral context not available from the annotations alone.

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 description is three sentences, front-loaded with purpose, followed by the resume behavior and the 410 failure case. Every sentence carries useful information and there is no redundant repetition of the schema or annotations.

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 two-parameter write tool with full schema coverage and annotations covering safety/idempotency, the description is mostly complete: it explains the core action, resume behavior, and a notable 410 error. One minor gap remains around what happens when a human request is pending, but this is a small omission rather than a major ambiguity.

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%, and both parameters are documented in the schema. The description adds no additional semantics about run_id or message beyond what the schema already provides, so the baseline score of 3 applies.

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 states a specific verb and resource: 'Post a message to an agent run.' It also clarifies that the message is persisted and may resume execution. It does not explicitly name or contrast with siblings such as listRunMessages or respondToHumanRequest, so it falls short of full sibling differentiation.

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?

Usage is implied by the purpose and by the resume condition: the agent will resume only if the run is completed or interrupted and has no pending human request. However, the description does not explicitly say when to use this instead of alternatives like respondToHumanRequest, nor does it clearly state whether posting is allowed while a human request is pending.

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