Customizing the system prompt

The base system prompt teaches the model to behave as a map assistant. It covers who it is, what it can do, how to decline out-of-scope requests, how to format answers and treat incomplete data, how to call tools, and how session state works. Instead of replacing it, prepend a preamble, append instructions or override individual sections while the others keep their defaults.

How a prompt is assembled

The base prompt has seven named sections, exported as SYSTEM_PROMPT_SECTIONS. In order, createMapAgent assembles your optional systemPromptPrefix, the base sections with any overrides, and your optional systemPromptSuffix under an ADDITIONAL INSTRUCTIONS: heading.

Prefix, suffix and section overrides work together. A full-string systemPrompt replaces the whole grey box and ignores the prefix and suffix.

The sections

Per-tool mechanics (coordinate order, "near me" vs "in this area") live in the tool descriptions and the classifier prompt, so they stay correct as tools change.

What the prompt doesn’t reach

The system prompt goes only to the main model, never to the intent classifier, which picks each turn’s tools from their classificationPrompt. So “always also call getTrafficIncidents” has no effect on a turn where the classifier didn’t pick that tool:

• To change when a tool is offered, extend its classificationPrompt. See Per-tool classification prompts.
• To offer it on every turn, set alwaysActive: true on its entry.
• Then use the prompt to tell the model when to call it.

Four ways to shape it

Choose the least invasive option. Nudge with the prefix or suffix, retune with section overrides, and replace the prompt only when you must remove base behaviour.

Prepend or append

systemPromptPrefix and systemPromptSuffix keep the whole base prompt, so your agent gets base refinements when you upgrade.

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const agent = createMapAgent(map, {
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    model: openai('gpt-4o'),
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    systemPromptPrefix: 'You work for Acme Logistics.',
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    systemPromptSuffix: 'Always respond in Spanish. Never show more than 5 places at once.',
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});

Override individual sections

Pass a SystemPromptSectionOverrides object as systemPrompt. Each key replaces that section’s body, and the SDK adds the heading. Sections you leave out keep their defaults. An empty string drops the section, including its heading:

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const agent = createMapAgent(map, {
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    model: openai('gpt-4o'),
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    systemPrompt: {
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        identity: 'You are a delivery fleet dispatcher built on the TomTom map.',
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        responseFormatting: 'Reply in Dutch, metric units, one short paragraph.',
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        dataConfidence: '', // dropped
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        // capabilities, rejectionRules, toolExecution, sessionState stay default
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    },
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});

Extend a default section

To add to a section instead of replacing it, read its default from SYSTEM_PROMPT_SECTIONS and derive a new value. Use this to append one rule, or to hand the default to a coding agent to rewrite under some criteria:

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import { createMapAgent, SYSTEM_PROMPT_SECTIONS } from '@tomtom-org/maps-sdk-plugin-agent-toolkit';
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const agent = createMapAgent(map, {
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    model: openai('gpt-4o'),
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    systemPrompt: {
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        rejectionRules: `${SYSTEM_PROMPT_SECTIONS.rejectionRules}\n- Decline weather questions.`,
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    },
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});

composeSystemPrompt(overrides) returns the assembled string for logging, diffing or a token-budget check. If you pass it back as systemPrompt, it is a full string, so the agent ignores the prefix and suffix.

The site selection agent example replaces identity and capabilities and extends rejectionRules for a narrowly scoped agent.

Full replacement

With a full replacement, you own the entire prompt and re-check the base on each upgrade. Extend BASE_SYSTEM_PROMPT instead of starting from scratch. Its sections carry the guidance that keeps the agent reliable.

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import { createMapAgent, BASE_SYSTEM_PROMPT } from '@tomtom-org/maps-sdk-plugin-agent-toolkit';
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const agent = createMapAgent(map, {
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    model: openai('gpt-4o'),
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    systemPrompt: BASE_SYSTEM_PROMPT + `
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ADDITIONAL INSTRUCTIONS:
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- This is a logistics application. Prioritize route efficiency over scenery.
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- Always show estimated arrival times in responses.
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- When a vehicle ID is mentioned, call getFleetVehicle before anything else.
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`,
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});

Keeping a persona prompt lean

Section overrides keep the base scaffolding around your persona text, so the result can be longer than a hand-written prompt. If size matters, don’t restate what the base sections cover. Override only where the persona differs, for example a one-line rejectionRules instead of the multi-bullet default, or '' to drop a section. composeSystemPrompt(overrides).length gives the assembled length.

Related

• Securing your agent — why the prompt is public, and why it is not the place for credentials, internal detail or a spending rule.
• How it works — where the assembled prompt is used in a turn.
• Customizing tools — shaping the registry the prompt describes.