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OverviewDiscussionsAdmin

Publish or schedule a post

create_post
Idempotent

Publishes to every named channel, or schedules it with scheduledAt. THIS IS PUBLIC AND CANNOT BE UNDONE once a network has published. idempotencyKey is required: derive it from the content or the task, not at random, so a timeout you retry returns the original post instead of publishing a second one. Under a review-mode credential this prepares the post and stops for a person to approve.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
draftNoKeep it in Mellow as a draft. Nothing is sent to any network.
mediaNoOrdered media. Each entry is a public https URL, or an object with url and an optional thumbnailUrl.
captionNoThe text of the post. Networks with shorter limits can be given their own with perChannel.
optionsNoPer-network settings, keyed by platform: instagram, facebook, threads, tiktok, tiktok_business, youtube, x, linkedin, pinterest, bluesky. YouTube requires title. Pinterest pins to the account's first board unless boardIds names one, and a Pinterest video needs a cover: thumbnailUrl on the media item. Instagram and Facebook take placement (timeline, reels, stories). A TikTok that promotes the owner's own product or business takes discloseYourBrand: true (TikTok labels it Promotional content); one another brand paid for takes discloseBrandedContent: true. See mellow://guide/platforms for every field.
channelsYesChannel IDs from list_channels, each beginning spc_.
perChannelNoOverrides for one channel, keyed by channel ID. Accepts caption, media, and that network's options. This is how you give one channel a shorter caption without shortening the post everywhere.
scheduledAtNoISO 8601 time to publish at. Omit to publish immediately.
idempotencyKeyYes8–120 characters, stable for this post. Reusing it for different content is refused.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changed
    • changedInput schema / properties / options / description
      Previous value: -"Per-network settings, keyed by platform: instagram, facebook, threads, tiktok, tiktok_business, youtube, x, linkedin, pinterest, bluesky. YouTube requires title. Pinterest pins to the account's first board unless boardIds names one, and a Pinterest video needs a cover: thumbnailUrl on the media item. Instagram and Facebook take placement (timeline, reels, stories). See mellow://guide/platforms for every field."New value: +"Per-network settings, keyed by platform: instagram, facebook, threads, tiktok, tiktok_business, youtube, x, linkedin, pinterest, bluesky. YouTube requires title. Pinterest pins to the account's first board unless boardIds names one, and a Pinterest video needs a cover: thumbnailUrl on the media item. Instagram and Facebook take placement (timeline, reels, stories). A TikTok that promotes the owner's own product or business takes discloseYourBrand: true (TikTok labels it Promotional content); one another brand paid for takes discloseBrandedContent: true. See mellow://guide/platforms for every field."
  2. Changed2 schema fields changed
    • changedInput schema / properties / media / items / anyOf
      Previous value: -[
-  {
-    "description": "A public https URL.",
-    "type": "string"
-  },
-  {
-    "properties": {
-      "thumbnailTimestampMs": {
-        "description": "Milliseconds into the video to take a poster frame from.",
-        "type": "number"
-      },
-      "thumbnailUrl": {
-        "description": "Poster frame, where the network accepts one.",
-        "type": "string"
-      },
-      "url": {
-        "description": "A public https URL.",
-        "type": "string"
-      }
-    },
-    "required": [
-      "url"
-    ],
-    "type": "object"
-  }
-]New value: +[
+  {
+    "description": "A public https URL.",
+    "type": "string"
+  },
+  {
+    "properties": {
+      "tags": {
+        "description": "Accounts marked on this item. Instagram and Facebook only, at most 20. Not the same as options.instagram.collaborators: a collaborator co-owns the post and it appears on their profile, a tag marks somebody on the picture. A bare string is an Instagram username.",
+        "items": {
+          "anyOf": [
+            {
+              "description": "An Instagram username.",
+              "type": "string"
+            },
+            {
+              "properties": {
+                "id": {
+                  "description": "Instagram username, Facebook user id, or Instagram product id.",
+                  "type": "string"
+                },
+                "kind": {
+                  "description": "Defaults to user. Products are Instagram only.",
+                  "enum": [
+                    "user",
+                    "product"
+                  ],
+                  "type": "string"
+                },
+                "platform": {
+                  "description": "Defaults to instagram.",
+                  "enum": [
+                    "instagram",
+                    "facebook"
+                  ],
+                  "type": "string"
+                },
+                "x": {
+                  "description": "Fraction from the left edge, 0 to 1. Send with y, or neither.",
+                  "type": "number"
+                },
+                "y": {
+                  "description": "Fraction from the top edge, 0 to 1. Videos and stories take no position.",
+                  "type": "number"
+                }
+              },
+              "required": [
+                "id"
+              ],
+              "type": "object"
+            }
+          ]
+        },
+        "maxItems": 20,
+        "type": "array"
+      },
+      "thumbnailTimestampMs": {
+        "description": "Milliseconds into the video to take a poster frame from.",
+        "type": "number"
+      },
+      "thumbnailUrl": {
+        "description": "Poster frame, where the network accepts one.",
+        "type": "string"
+      },
+      "url": {
+        "description": "A public https URL.",
+        "type": "string"
+      }
+    },
+    "required": [
+      "url"
+    ],
+    "type": "object"
+  }
+]
    • changedInput schema / properties / options / description
      Previous value: -"Per-network settings, keyed by platform: instagram, facebook, threads, tiktok, tiktok_business, youtube, x, linkedin, pinterest, bluesky. YouTube requires title. Pinterest requires boardIds. Instagram and Facebook take placement (timeline, reels, stories). See mellow://guide/platforms for every field."New value: +"Per-network settings, keyed by platform: instagram, facebook, threads, tiktok, tiktok_business, youtube, x, linkedin, pinterest, bluesky. YouTube requires title. Pinterest pins to the account's first board unless boardIds names one, and a Pinterest video needs a cover: thumbnailUrl on the media item. Instagram and Facebook take placement (timeline, reels, stories). See mellow://guide/platforms for every field."
  3. Changed2 schema fields changed
    • changedInput schema / properties / media / items / anyOf
      Previous value: -[
-  {
-    "description": "A public https URL.",
-    "type": "string"
-  },
-  {
-    "properties": {
-      "tags": {
-        "description": "Accounts marked on this item. Instagram and Facebook only, at most 20. Not the same as options.instagram.collaborators: a collaborator co-owns the post and it appears on their profile, a tag marks somebody on the picture. A bare string is an Instagram username.",
-        "items": {
-          "anyOf": [
-            {
-              "description": "An Instagram username.",
-              "type": "string"
-            },
-            {
-              "properties": {
-                "id": {
-                  "description": "Instagram username, Facebook user id, or Instagram product id.",
-                  "type": "string"
-                },
-                "kind": {
-                  "description": "Defaults to user. Products are Instagram only.",
-                  "enum": [
-                    "user",
-                    "product"
-                  ],
-                  "type": "string"
-                },
-                "platform": {
-                  "description": "Defaults to instagram.",
-                  "enum": [
-                    "instagram",
-                    "facebook"
-                  ],
-                  "type": "string"
-                },
-                "x": {
-                  "description": "Fraction from the left edge, 0 to 1. Send with y, or neither.",
-                  "type": "number"
-                },
-                "y": {
-                  "description": "Fraction from the top edge, 0 to 1. Videos and stories take no position.",
-                  "type": "number"
-                }
-              },
-              "required": [
-                "id"
-              ],
-              "type": "object"
-            }
-          ]
-        },
-        "maxItems": 20,
-        "type": "array"
-      },
-      "thumbnailTimestampMs": {
-        "description": "Milliseconds into the video to take a poster frame from.",
-        "type": "number"
-      },
-      "thumbnailUrl": {
-        "description": "Poster frame, where the network accepts one.",
-        "type": "string"
-      },
-      "url": {
-        "description": "A public https URL.",
-        "type": "string"
-      }
-    },
-    "required": [
-      "url"
-    ],
-    "type": "object"
-  }
-]New value: +[
+  {
+    "description": "A public https URL.",
+    "type": "string"
+  },
+  {
+    "properties": {
+      "thumbnailTimestampMs": {
+        "description": "Milliseconds into the video to take a poster frame from.",
+        "type": "number"
+      },
+      "thumbnailUrl": {
+        "description": "Poster frame, where the network accepts one.",
+        "type": "string"
+      },
+      "url": {
+        "description": "A public https URL.",
+        "type": "string"
+      }
+    },
+    "required": [
+      "url"
+    ],
+    "type": "object"
+  }
+]
    • changedInput schema / properties / options / description
      Previous value: -"Per-network settings, keyed by platform: instagram, facebook, threads, tiktok, tiktok_business, youtube, x, linkedin, pinterest, bluesky. YouTube requires title. Pinterest pins to the account's first board unless boardIds names one, and a Pinterest video needs a cover: thumbnailUrl on the media item. Instagram and Facebook take placement (timeline, reels, stories). See mellow://guide/platforms for every field."New value: +"Per-network settings, keyed by platform: instagram, facebook, threads, tiktok, tiktok_business, youtube, x, linkedin, pinterest, bluesky. YouTube requires title. Pinterest requires boardIds. Instagram and Facebook take placement (timeline, reels, stories). See mellow://guide/platforms for every field."
  4. Changed1 schema field changed
    • changedInput schema / properties / options / description
      Previous value: -"Per-network settings, keyed by platform: instagram, facebook, threads, tiktok, tiktok_business, youtube, x, linkedin, pinterest, bluesky. YouTube requires title. Pinterest requires boardIds. Instagram and Facebook take placement (timeline, reels, stories). See mellow://guide/platforms for every field."New value: +"Per-network settings, keyed by platform: instagram, facebook, threads, tiktok, tiktok_business, youtube, x, linkedin, pinterest, bluesky. YouTube requires title. Pinterest pins to the account's first board unless boardIds names one, and a Pinterest video needs a cover: thumbnailUrl on the media item. Instagram and Facebook take placement (timeline, reels, stories). See mellow://guide/platforms for every field."
  5. First observed

TDQS

A3.9/5.0
Behavior4/5

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

Goes well beyond the annotations: it warns the post is public, cannot be undone once a network publishes, explains the review-mode credential path, and tells the agent how to derive idempotencyKey rather than just that the call is idempotent. It omits things like rate limits or partial-failure behavior across channels, so not a 5.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three tightly packed sentences, no filler, and the highest-stakes fact (public, irreversible) is front-loaded before the idempotency and review-mode details.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a mutating, open-world publishing tool it covers the critical risks: public exposure, irreversibility, idempotency, and approval mode. With no output schema, it does not say what a successful call returns (e.g., post identifiers the caller would need for get_post/post_results), which is the main remaining gap.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is already 100%, so the baseline is 3, but the description adds real meaning on idempotencyKey ('derive it from the content or the task, not at random') that the schema's 'stable for this post' does not convey. Other params (draft, media, perChannel) are left entirely to the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Publishes to every named channel, or schedules it with scheduledAt'), plus the scope that all named channels receive the post. It implicitly separates itself from preview_post/validate_post via the irreversibility warning, but never names a sibling, so it stops short of a 5.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The publish-now vs schedule-with-scheduledAt fork is stated, and the review-mode note tells the agent what happens under certain credentials. However, it never directs the agent to validate_post or preview_post first, and gives no explicit when-not to call it, leaving the alternatives to inference.

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

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