Before distributing an agent skill with an executable helper, define how the recipient gets the interpreter, dependency manager and resolved packages that the helper needs. Keep ordinary execution separate from permission to change that environment. A script that works on the author’s machine may be relying on resources absent from the delivered package.
For teams maintaining actual SKILL.md packages, the decision is what execution arrangement they support. Identify the approved runtime, dependency record, installation route and behavior when a prerequisite is unavailable. Then check those conditions using the distributed artifact rather than assuming a successful author-side demonstration will transfer.
This guide proposes a runtime review for a fictional spreadsheet helper. It does not report a skill installation, dependency installation, assistant trial or executed helper test. Commands mentioned below describe documented tooling; they are not a tested setup recipe for your assistant surface.
Treat compatibility metadata as a declaration
The Agent Skills specification defines compatibility as an optional field for environment requirements, including products, system packages and network access. A package can also contain scripts and supporting resources. Declaring that a skill requires Python and a package manager does not establish that the host provides either one.
Write the requirement in terms an operator can verify. “Requires Python” leaves open which supported version, how it is selected and whether the intended environment permits subprocess execution. “Install dependencies if needed” also leaves open the source, scope and authority for the installation.
Avoid having the agent repair an unfamiliar environment by improvising global package changes. Use the organization’s established provisioning route and standing permissions. If those do not cover an installation, return the specific missing prerequisite and the supported next step. A readable skill remains useful documentation even where its helper cannot execute, but those are different capabilities.
Our package-relocation guide addresses finding bundled resources after moving the package. This guide addresses the software environment required once those files have been found.
Separate a dependency range from its resolved environment
Imagine a fictional skill that converts an approved spreadsheet into a service-summary draft. It bundles a Python helper and a template. The helper needs an approved spreadsheet-reading library; it does not upload documents or modify the source workbook.
The author could declare acceptable library versions in the script. That describes what may be selected. It does not, by itself, record the complete selection made for a particular delivery, including dependencies pulled in by that library.
Astral’s uv script guide documents inline dependency metadata and explicit script locking. Running uv lock --script example.py creates an adjacent example.py.lock. Subsequent operations can reuse that lock and may update it when necessary. The guide separately documents Python-version selection. These are uv-specific behaviors, not requirements enforced by the Agent Skills format.
For the fictional helper, deliver the dependency record that matches the script, and document the execution mode that is supposed to preserve it. If ordinary execution is allowed to resolve a different environment, describe that honestly. Do not call a changing resolution a fixed release merely because the top-level script is unchanged.
An exact top-level package version is also a narrower statement than a reviewed environment. Check the dependency manager’s treatment of transitive packages, platform-specific artifacts and interpreter requirements. Retain enough information to identify what was actually installed when investigating a failure.
Lock enforcement and network availability answer different questions
Martin Mahner’s April 2026 practitioner post on script locking recommends carrying a lockfile with the script and using explicit runtime controls. Its practical contribution is to distinguish inline version constraints from a resolved dependency record. It is not evidence that the proposed skill works in any particular assistant.
Use the current uv command reference for the precise controls. --locked requires an up-to-date lock; --frozen uses the lock without updating it or checking its freshness in the same way. The separate --offline option limits uv to locally cached data and available files. Preventing lock updates is not the same as making dependency artifacts available offline.
That distinction matters for the spreadsheet helper. A previously prepared machine may have every dependency cached. A fresh machine may need authorized downloads before it can run the identical selection. The lockfile records a resolution; it is not a bundled copy of every required file.
Also distinguish the package manager’s network behavior from the helper’s behavior. A package-manager offline option does not establish a network sandbox around arbitrary code launched afterward. Where network isolation is required, verify the execution environment’s actual controls and inspect the helper’s intended data path.
Choose these controls deliberately for the supported tool version. A deployment that must detect stale declarations has a different acceptance condition from one that intentionally executes an already approved lock as the source of truth. Verify the exact command in that environment before publishing operational instructions.
Test the missing resources, not just the successful cache
For the fictional helper, the owner could define the following acceptance cases. These are proposed tests, not observations from runs performed for this article.
| Proposed condition | What the owner needs to establish |
|---|---|
| Prepared environment with approved dependencies | Expected summary from the controlled workbook |
| Fresh supported environment | Documented provisioning succeeds within the allowed installation and network policy |
| Required interpreter or runner absent | Identifiable prerequisite failure without improvised substitution |
| Script declaration changed while lock remains old | The chosen validation mode detects or handles the mismatch as specified |
| Lock omitted from the delivered package | Failure or explicitly permitted resolution, according to the release contract |
| Required artifact unavailable with downloads disabled | Clear availability failure rather than an apparently completed report |
Keep the workbook and expected summary constant while checking the environment. Include a deliberately incompatible prerequisite so that the test can reveal a hidden fallback. An agent silently using another library or rebuilding the workflow in prose has changed the procedure, even if its output looks plausible.
Do not create a cold-cache test by clearing a shared production cache. Use a disposable, appropriately controlled test environment. Record the interpreter, dependency-manager version, platform, installed selection and provisioning outcome. Then test the helper’s business behavior separately: consistent installation does not establish correct spreadsheet interpretation.
Repeatability still has a scope
The 2024 paper Reproducibility of Build Environments through Space and Time studies historical Nix environments and rebuilding older software. Its methodology distinguishes environment evaluation from actual rebuilding and explains the role of cached dependencies. It also identifies limitations in extending the results, including reliance on the cache and not checking bit-for-bit reproducible outputs in that evaluation.
This is research on Nix, not a validation of uv, agent skills or our fictional helper. It informs a narrower review question: which inputs and available resources does the reproducibility claim actually cover? We do not import its success rates into a skill compatibility claim.
For a business helper, the environment record may still omit external executables, operating-system libraries, remote services or changing input data. Identify the ones the task depends on. Pinning Python packages does not freeze a connected service or make generated prose deterministic.
Keep claims specific: “this helper produced the expected fixture output in this documented environment” is an inspectable result once tested. “This skill works everywhere” is not supported by one installation or one lockfile.
Make dependency updates a reviewed change
Maintain a known-good script and dependency record together. When a dependency changes, regenerate the appropriate record through the normal review process, inspect the change and rerun relevant controlled cases. Preserve the previous supported combination where recovery requires it.
An old lock is not automatically a safe lock. Continue the organization’s dependency maintenance and security review; reproducibility preserves a selection, including its defects. Our dependency-identity guide covers establishing which software a generated installation instruction refers to. That review remains separate from whether the chosen environment can be reconstructed.
Start with one distributed helper. Ask a colleague or test system to provision it from the delivered files in a fresh supported environment, then exercise the missing-prerequisite cases. Record the actual boundaries before promising repeatable execution to the next team.