Simulate a Stellar transaction to predict its results and costs before submitting it on testnet, mainnet, futurenet, or local networks.
Simulate a transaction to predict results and costs
| Name | Required | Description | Default |
|---|---|---|---|
| tx_xdr | Yes | Transaction XDR to simulate (base64) | |
| network | Yes | Stellar network | |
| source_account | No | Source account for simulation context |
Changes observed during successful MCP inspections.
v1.0.1Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full burden of behavioral disclosure. It never states that the transaction is not submitted or state changed, what 'costs' encompasses (fees, resource/compute units), or whether simulation can fail on unfunded accounts. For a no-annotation tool this is a meaningful gap.
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?
A single front-loaded sentence with zero filler, so it is efficient. It is arguably too terse for a tool with no annotations and no output schema, but nothing in it is wasted.
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?
With no annotations and no output schema, the description should explain what the simulation returns and any operational caveats. 'Predict results and costs' is too abstract for an agent to know whether it gets fee estimates, error diagnostics, or ledger effects.
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%, so the schema already documents tx_xdr (base64), the network enum, and source_account. The description adds no syntax, format, or constraint detail beyond that, which is the expected baseline when the schema does the heavy lifting.
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 names a specific verb (simulate) and resource (transaction) plus the outcome (predict results and costs), so an agent knows this is a dry-run evaluator rather than a submitter. It does not explicitly contrast itself with the closely related siblings stellar_tx_send or stellar_tx_decode, leaving differentiation to inference from the name.
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?
There is no when-to-use guidance, no prerequisites (e.g. a funded source account or valid XDR), and no mention of alternatives such as stellar_tx_send for actually broadcasting. The agent must infer that this is the pre-flight check from the word 'simulate' alone.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.