Portainer Portainer MCP Portainer MCP Hygiene

Portainer MCP hygiene

The Portainer MCP server returns large JSON payloads by default — a list of environments with snapshots, a list of K8s pods with full status blocks, a stack with its complete manifest. Every tool the server exposes accepts an optional select (JMESPath) parameter applied server-side before the response reaches you. Responses are capped at ~50,000 chars; if you exceed the cap you get a truncation hint that names select and shows an example.

The cost of not projecting is real: 50K chars of dense JSON eats roughly 20K tokens out of your context for a question that usually needed a few hundred. Once truncation fires, you've wasted a round trip and the data past the cap is gone for that call. The default move on any list-shaped Portainer call is to pass select from the start.

Resolve the environment first

Both proxy tools take an environment_id, and the IDs aren't predictable — they're assigned in creation order, not "local = 1". So for any environment-scoped question, resolve the target first with one call:

EndpointList(select="[].{id:Id,name:Name,type:Type,status:Status}")

and use the ID whose name matches what the user means. Guessing the environment is a hard failure, not a silent one: a wrong ID makes the proxy raise an API request failed (HTTP 404) error rather than returning empty data — so a wrong environment is not a source of null projections. Two other things are, though: an unquoted dotted key (see the JMESPath notes below) and a field-name mismatch on the typed GetAllKubernetes* tools (see their note under Where the noise lives). So read an all-null result as a wrong-keys signal to investigate, not as proof the data is absent.

The default pattern

For any call that returns a list of objects, ship a JMESPath that keeps only the fields the user's question actually needs:

EndpointList(select="[].{id:Id,name:Name,type:Type,status:Status}")
docker_proxy(environment_id=N, path="/containers/json", select="[].{id:Id,name:Names[0],state:State,image:Image}")
kubernetes_proxy(environment_id=N, path="/api/v1/pods", select="items[].{name:metadata.name,ns:metadata.namespace,phase:status.phase,node:spec.nodeName}")

JMESPath syntax notes that matter for these surfaces:

• List shape: start with [] to map over array elements.
• Wrapped list (Kubernetes {items: [...]}): start with items[].
• Single object: {field1:path.to.value,field2:other.path} — no leading [].
• Nested paths use dots: Snapshots[0].RunningContainerCount. But a key that itself contains a dot or hyphen — compose labels, K8s annotations — collides with that syntax, so quote it as an identifier: Labels."com.docker.compose.project", or in a filter [?Labels."com.docker.compose.project"=='myproj']. Unquoted, JMESPath reads the dots as nested keys and silently returns null — which looks like a missing field rather than a broken expression. Quote with double quotes, not backslashes (\"…\" fails to parse) and not backticks (those denote JSON literals).

Where the noise lives

These are the fields/sections that dominate Portainer payloads. Either project them out (when you don't need them) or project specifically into them (when they are the answer):

EndpointList — .Snapshots[0] carries the heavy payload. Each environment includes a full Docker or Kubernetes snapshot — container list, image list, network list, etc. For counts and status questions you almost always want to project into specific snapshot fields rather than fetch them whole:

# Container counts per environment
EndpointList(select="[].{name:Name,running:Snapshots[0].RunningContainerCount,total:Snapshots[0].ContainerCount}")

# Just identity + status field
EndpointList(select="[].{id:Id,name:Name,type:Type,status:Status}")

Status is the right reachability signal only for direct agents — for edge environments it stays 0 regardless of health. See Interpreting results, not just shrinking them below before reading it as up/down.

Kubernetes via kubernetes_proxy — metadata.managedFields and status are huge. metadata.managedFields alone is routinely 30-70% of an object. The status block on Deployments, StatefulSets, Pods, and Nodes is similarly verbose. Project them out unless the user is asking about reconciliation state or controller history:

# Pod summary
kubernetes_proxy(environment_id=N, path="/api/v1/pods", select="items[].{name:metadata.name,ns:metadata.namespace,phase:status.phase,restarts:status.containerStatuses[0].restartCount,node:spec.nodeName}")

# Deployment readiness
kubernetes_proxy(environment_id=N, path="/apis/apps/v1/deployments", select="items[].{name:metadata.name,ns:metadata.namespace,replicas:spec.replicas,ready:status.readyReplicas}")

GetAllKubernetes* tools — full object body per element, in a Portainer-specific shape. The OpenAPI-generated GetAllKubernetesApplications, GetAllKubernetesPersistentVolumes, GetAllKubernetesConfigMaps, etc. return arrays where each element carries its full body — so project to the fields you need. But mind the field names: these typed tools do not use the raw-K8s paths the proxy uses (metadata.name, status.phase, spec.…), and they don't reliably match the PascalCase of EndpointList (Id, Name) either. They tend to be flattened camelCase, and some fields collapse — e.g. GetAllKubernetesPersistentVolumes returns identity as a top-level name (not metadata.name) and status as a bare string "Bound" (not status.phase):

# Actual shape — camelCase, flattened, status-as-string
GetAllKubernetesPersistentVolumes(select="[].{name:name,status:status,claimNs:claimRef.namespace,sc:storageClassName,reclaim:persistentVolumeReclaimPolicy}")

Because the convention varies by tool, an all-null projection here almost always means you guessed the wrong keys — reusing the proxy's metadata.name or EndpointList's Name — not that the data is absent. When unsure, fetch one element with no select first to read the real field names, then project. If you'd rather work in raw-K8s field names, use kubernetes_proxy instead.

StackList and StackInspect — config and env vars. Stacks carry the full compose/manifest content plus environment variable dictionaries. If the user asked "which stacks exist?", project to {id, name, type, status}. If they asked about a specific stack's config, fetch it directly and only then look at the body. Env values come back redacted by default — see Env values are redacted by default below.

Snapshot inspects (snapshotInspect, snapshotContainersList, etc.) — entire snapshots. These return the whole snapshot blob by design. Always project.

Helm endpoints — full chart values and manifests. HelmList carries release status + chart metadata; HelmGet returns the rendered manifest. Project to release names and status when listing; only fetch the manifest when the user asked to see it.

EndpointGetCharts, dockerDashboard, EndpointSummaryCounts — already aggregated. These are the lightweight "summary" tools. Prefer them over EndpointList + projection when the user's question is purely a count or rollup — fewer characters, less work, more accurate (server-side aggregation).

Env values are redacted by default. Stack, container, and Kubernetes env values come back as [REDACTED]. The response also carries a one-line summary: [N env value(s) redacted; set PORTAINER_EXPOSE_ENV_VALUES=1 on the MCP server to disclose].

• Don't waste a tool call fishing for them via select — the projection runs after redaction, so any field path lands on the sentinel.
• If the user genuinely needs an env value (troubleshooting a deploy), tell them to set PORTAINER_EXPOSE_ENV_VALUES=1 on the MCP server and reconnect. Don't invoke the toggle yourself.
• The sentinel [REDACTED] is a literal placeholder — never quote it back to the user as if it were the real value.
• Redaction covers Env / EnvVars shapes (stack Env pairs, Docker KEY=VAL strings, K8s env[].value). K8s valueFrom references are preserved — they're references to a Secret/ConfigMap, not the secret material itself.

Interpreting results, not just shrinking them

Projecting the right fields only helps if you read them correctly. The highest-frequency misread on this surface:

Edge environments — Status is not the health signal; Heartbeat is. The endpoint Status field means up/down only for direct agents (1 = up, 2 = down). For edge agents (Type 4 = EdgeAgentOnDocker, 7 = EdgeAgentOnKubernetes) Status is left at its zero value 0 and never tracks reachability — so reading Status: 0 as "down" is a false alarm. Portainer judges an edge agent by its heartbeat: up if it checked in within 2 × interval + 20 seconds (the interval is EdgeCheckinInterval, falling back to the global Edge check-in setting, for standard agents; the smallest of the ping/command/snapshot intervals for async agents). The server exposes this as a computed Heartbeat boolean — which is exactly what the dashboard's environment badge renders ("Heartbeat" vs "Down").

For a reachability check that's correct across both kinds, project the heartbeat inputs, not just Status:

EndpointList(select="[].{id:Id,name:Name,type:Type,status:Status,heartbeat:Heartbeat,lastCheckIn:LastCheckInDate}")

Read it as: direct agent → trust status (1 = up); edge agent (type 4/7) → trust heartbeat (true = up) and ignore status.

Patterns for common questions

A few high-frequency questions and the projection that gets them in one call:

"How many running containers in each environment?"

EndpointList(select="[].{name:Name,type:Type,running:Snapshots[0].RunningContainerCount,total:Snapshots[0].ContainerCount}")

"List containers in environment N."

docker_proxy(environment_id=N, path="/containers/json",
             select="[].{id:Id,name:Names[0],state:State,image:Image,status:Status}")

"Which images are in use, grouped by name?" Fetch with projection, group client-side:

docker_proxy(environment_id=N, path="/containers/json", select="[].Image")

"One-line pod summary in environment N."

kubernetes_proxy(environment_id=N, path="/api/v1/pods",
                 select="items[].{name:metadata.name,ns:metadata.namespace,phase:status.phase,node:spec.nodeName}")

"Which deployments aren't fully ready?" Project readiness fields, then filter in the response. (JMESPath can also filter inline with items[?status.readyReplicas != spec.replicas], but expressions like that are easy to get wrong — projection + your own filter is usually safer.)

"Inspect deployment X in namespace Y." A single-object fetch. Project out metadata.managedFields and status.conditions if you only need the spec; keep them if the user is asking about reconciliation:

kubernetes_proxy(environment_id=N, path="/apis/apps/v1/namespaces/Y/deployments/X",
                 select="{name:metadata.name,replicas:spec.replicas,ready:status.readyReplicas,image:spec.template.spec.containers[0].image}")

Non-JSON endpoints — select does not apply

A handful of docker_proxy and kubernetes_proxy paths return plain text or streamed data rather than JSON — logs, stats, exec output. On these the proxy detects the non-JSON body and passes it through unchanged, so any select you pass is silently ignored — a no-op, not an error, since there's no JSON to project. The response-size cap still applies, so a noisy stream can still truncate. Narrow the upstream query parameters instead of projecting.

Container logs — /containers/{id}/logs:

• Set tail to limit lines (tail=100 for the last hundred).
• Set since to limit time range (Unix timestamp).
• Always pass stdout=true and/or stderr=true — without them Docker rejects the call with a 400.
• Don't set follow=true — it streams indefinitely and will burn your context.

Kubernetes pod logs — kubernetes_proxy path /api/v1/namespaces/{ns}/pods/{pod}/log:

• Cap the output with tailLines (e.g. tailLines=100) and/or limitBytes — the K8s equivalents of Docker's tail. Both are query params.
• Add previous=true to read the prior container after a crash/restart — the current container may be too young to show what failed.
• In a multi-container pod, pass container=<name> to pick one (otherwise the API errors).
• Don't set follow=true — like the Docker case it streams without end. select is a no-op here too; the body is plain text.

Container stats — /containers/{id}/stats:

• Always pass stream=false to get a single snapshot. The streaming form is unbounded.

Container exec output — chunked stream.

• If you need command output, prefer docker_proxy against /containers/{id}/top for process listing, or run the command another way. Exec attach over HTTP returns multiplexed binary frames and won't render usefully through the cap.

Image pulls / archives / build context — binary or streamed.

• Don't fetch these through the proxy for inspection. Use the specific Portainer endpoints (endpointDockerhubStatus, ServiceImageStatus, dockerImagesList) which return parseable JSON summaries.

If the cap fires on a non-JSON endpoint, the truncation hint will suggest select — ignore that suggestion in this case and retry with narrower upstream parameters.

When not to project

Projecting isn't always right:

• Small single-object reads that you already know are under a few KB — SettingsInspect, MOTD, StatusInspect, systemVersion. Projecting just adds a round of cognitive overhead for no win.

• Exploratory scans where you don't know what you're looking for — "anything unusual in this stack's config", "is there an error somewhere in this deployment's status". Here you want the full body so you can scan for patterns. Pull the full object; if it truncates, narrow the path (one resource, not the whole list) rather than projecting fields.

• When the user asked for "everything" — sometimes they really do want the raw object. Respect that, but warn them once if you're about to retrieve something that will eat their context.

Reading the truncation hint

When you do hit the cap, the response ends with a bracketed [truncated: ... Retry with a JMESPath select ...] message that includes a concrete example. Your next move should almost always be: retry the same call with a select projection — not pivot to reading the spilled file with jq, not paginate by guessing offsets, not call a different tool. The server-side projection is cheaper (no re-fetch from Portainer if the data was already cached upstream, and far fewer tokens shipped back).

The exception is non-JSON endpoints (see above) — there, ignore the select suggestion and re-shape the upstream query instead.

Mutations: verify, recover, clean up

Most of this skill is about reading; the same care applies when you change things. The Portainer mutation tools have a few habits worth planning around.

Success is usually silent — verify out-of-band. Create/update/delete tools tend to return nothing useful: CreateKubernetesNamespace returns an empty body, and StackCreateKubernetesFile / StackDelete return {"Output":""} on success. An empty response is not proof of success — it's indistinguishable from a swallowed error. After any mutation, confirm with a read: list the resource or fetch it and check its status. Don't report "done" off a non-error alone.

When a name-based call misbehaves, fall back to id. Some …ByName convenience tools need parameters you can't supply through the MCP and will reject the call. The reliable pattern is list → act-by-id: resolve the object first (StackList with a {id,name,type} projection), then act on the numeric id (StackDelete). Reach for this whenever a name-based mutation errors on something you can't satisfy.

Deletions can leave orphans — check the reclaim policy. Deleting a PVC (or a stack that owns one) does not necessarily reclaim its storage: under a Retain storage class the underlying PersistentVolume is left behind in Released state, still holding disk. After deleting volume-backed resources, list /persistentvolumes (via kubernetes_proxy, for accurate field names) and delete the released PV with DeleteKubernetesPersistentVolumes if you meant to free the space — but only the one you intend, never a Bound PV another workload is using.

Restart by scaling, not by deleting the pod. There's no first-class scale tool, so to stop or restart a workload, merge-PATCH its replica count through the proxy:

kubernetes_proxy(environment_id=N, method="PATCH",
                 path="/apis/apps/v1/namespaces/{ns}/deployments/{name}",
                 headers={"Content-Type": "application/merge-patch+json"},
                 body='{"spec":{"replicas":0}}')

Scale to 0, confirm the pod is gone, then back to the target count. For any workload that must not run two copies at once — anything writing to a single shared volume, such as a game server, a database, or any app with non-shared backing storage — this scale-to-zero-then-up cycle is the only safe restart. Never raise replicas above one to "roll" such a workload: two pods writing the same volume can corrupt it.

Tool selection cheatsheet

• Environment-level summary (counts, status, reachability) → EndpointList with snapshot projection, or EndpointSummaryCounts/dockerDashboard if the question is purely aggregate.
• Docker things on a specific environment → docker_proxy. The OpenAPI-generated dockerContainerGpusInspect, containerImageStatus, etc. are specific helpers; use them when they directly answer the question, otherwise the proxy is more flexible.
• Kubernetes things on a specific environment → either the OpenAPI-generated GetAllKubernetes* / GetKubernetes* tools (Portainer-aware, often already filtered) or kubernetes_proxy (raw K8s API, full flexibility). Prefer the typed tool when it exists; fall back to the proxy for paths Portainer doesn't surface natively.
• Helm releases → HelmList, HelmGet, HelmGetHistory. Don't try to route Helm through the K8s proxy — Portainer's Helm tools see the release metadata the K8s API alone doesn't.
• Mutations (POST/PUT/DELETE) → only in read-write mode. If the server is in PORTAINER_READ_ONLY=1, non-GET calls are rejected at the tool with a clear error. Don't retry mutations as GET when this happens — surface the read-only state to the user. See Mutations: verify, recover, clean up above for verifying success and cleaning up after writes.

When the skill itself is wrong

If reality contradicts this skill — a select example fails to parse, redaction behaves differently than described, a documented tool is missing or renamed, the truncation hint doesn't match what's written here — offer to file an issue on portainer/portainer-mcp, the repo this skill ships from, so the gap gets fixed for everyone. Server misbehaviour (a tool errors on valid input, the cap or redaction is broken) belongs there too. That repo is the only destination this section covers: user errors, instance misconfiguration, and Portainer product bugs are out of scope — handle them in conversation, don't offer to file them anywhere.

First make sure the evidence points at the skill rather than at your own expression: re-run the verbatim example from this file, not your adaptation of it. A null projection usually means an unquoted dotted key in your own expression (see the JMESPath notes above), not a skill gap. Only a verbatim example failing, or behaviour that contradicts an explicit claim in this file, is reportable.

1. Offer once per session. One line — "this looks like a gap in the portainer-mcp-hygiene skill; want me to file an issue on portainer/portainer-mcp?" If declined, drop it for the rest of the session. If more mismatches surface later, fold them into the one offer (and one issue) rather than asking per finding.
2. Draft and scrub. Replace hostnames/IPs/URLs, usernames, and resource names with placeholders (<portainer-host>, <stack-name>); never include tokens, env values, or response dumps. Quote the failing line, not the whole response — short bodies also survive the prefilled-link fallback below.
3. Include: the skill version from the footer of this file; the Portainer version (systemVersion is one cheap call) and the mcp-portainer server version if the user knows it; a title prefixed [portainer-mcp-hygiene] for skill-guidance gaps (plain titles for server bugs); what the skill said (quote it); the tool call made (tool name
   • sanitized arguments including the select expression); what actually happened; and what you expected.
4. Show the draft, then file on approval — gh issue create --repo portainer/portainer-mcp --title … --body … if gh is available and authenticated; otherwise hand the user a prefilled link they can open themselves: https://github.com/portainer/portainer-mcp/issues/new?title=<url-encoded>&body=<url-encoded>. Never file silently.

Skill version: 2.42.5 (matches the mcp-portainer release tag this file shipped with).

Source: portainer/portainer-mcp — distributed by TomeVault.