Resend a previously sent message. Loads the original send request and enqueues a brand-new send to the same recipient with the same content, producing a new messageId; the original message is unchanged. Rate limited per message (429 on rapid repeats).
| Name | Required | Description | Default |
|---|---|---|---|
| message_id | Yes | The message ID of the original message to resend |
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The annotations only say readOnlyHint=false, idempotentHint=false, and destructiveHint=false. The description meaningfully adds behavior: it loads the original send request, enqueues a new send, creates a new messageId, leaves the original message unchanged, and includes a rate-limit warning with a 429 code. This is substantial context beyond the structured annotations and aligns with the non-idempotent hint.
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 with no filler: the core purpose is front-loaded, the behavioral mechanism and side effects follow, and the rate-limit caution is compactly stated. Every sentence earns its place.
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?
This is a simple single-parameter tool with no output schema. The description covers the operation's purpose, side effects (new messageId, original unchanged), and an important operational constraint (429 rate limit). An agent has enough to invoke it correctly and anticipate consequences.
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 the single parameter message_id is already described as 'The message ID of the original message to resend.' The main description reinforces the parameter's role by explaining that the original send request is loaded, but it does not add significantly new semantic detail beyond what the schema already provides. Baseline 3 is appropriate.
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 opens with a precise verb and resource: 'Resend a previously sent message.' It clearly distinguishes this from siblings like send_message and send_message_to_list by emphasizing 'previously sent' and the fact that it creates a 'brand-new send' with a 'new messageId.' An agent can tell this tool apart without inspecting sibling schemas.
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 description clearly conveys the context: use this when resending a previously sent message, and the behavioral explanation that it reuses the original request makes the use case unambiguous. However, it does not explicitly name alternatives or state when NOT to use it, such as 'use send_message for new content,' 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.
Add one secure layer between your agents and this server.
Tools are mostly organized as distinct resource/action pairs, but several clusters are easy to confuse: list subscription tools (add_subscribers_to_list vs bulk_subscribe_to_list vs subscribe_user_to_list), message vs message-content vs message-history retrieval, and the many journey/journey-template list/get tools. Detailed descriptions rescue most selections, but the sheer number of near-identical verb/resource names creates real misselection risk.
Almost all tools follow a snake_case verb_noun pattern (create_, get_, list_, replace_, send_, publish_, archive_). Minor deviations keep it from a perfect score: courier_installation_guide is noun-first, and add_bulk_users sits awkwardly next to the bulk_add_* family, but the overall convention is predictable and readable.
144 tools is an extreme working-set size for an agent to hold and choose from, far beyond the reasonable 3–15 range. Even for a broad platform like Courier, this should be split into focused sub-servers (templates, journeys, users, lists, preferences, etc.) to remain usable.
The surface is remarkably comprehensive, covering sending, templates, journeys, automations, users, tenants, lists, preferences, providers, routing, brands, audiences, translations, digests, bulk jobs, and audit events. Notable gaps exist—automation template CRUD and digest schedule management are missing—but most workflows can still be completed with workarounds.
